GASTROPODS, SCAPHOPODS, PE LECYPODS: NUC'ULIDAE TO MALLEIDAE52


Not Glycymeris canalig Brown and Pilsbry, Maury, Bull. Am.
 Paleontology, v. 10, no. 42, p. 31, pl. 18, figs. 3, 4, 1925
 (M.Niocene, Trinidad).
 Of medium size, trigonal-ovate, umbonal area narrow, its margins sloping. Height equal to length, or slightly greater than length, posterior margin slightly extended. Sculptured with 22 to 31 (generally 30) low, arched primary ribs of moderate width, wider than space between them; space between ribs exceptionally very niarrow. Ribs generally f ading out near upper margin-s. Minor secondary sculpture appearing ait height of 10 to 20 mm: an interstitial narrow rib or thread in some spaces between ribs, especially anterior ribs, generally at edge of space immediately adjoining primary rib, exceptionally in middle of space. On unworn surfaces fine, closely spaced concentric threads on ribs and in space between them. "Resting stages" conspicuous on many shells, especially those of large size. Cardinal area short, narrow, amphildetic.
 Length 34.6 mm, height 36 mim, diameter 11 mm (figured right valve).
 Type material: Lectotype, herewith designated, the specimen illustrated by Brown and Pilsbry, the largest of four in the type lot, Acad. Nat. Sci. Philadelphia 1747.
 Type locality: Gatun. Locks excavation, Canal Zone, middle part of Gatun f ormation.
 Though the upper part of the Gatun formation yielded two immature valves of Glycymeris pectinata canali8, the remaining 31 specimens identified without qualification are f rom the middle part. Collections from the Gatun Third Locks excavation are the most satisfactory and include the only fully mature v-alves. Eighteen specimens in one of those collections (155b) represent a growth series f rom a length of 9.8 to 35 mmn. Eight valves from the La Boca formation, ranging inl length from 9 to 21.8 mm, and an external miold from the lower member of the AlhIajuela formation (length 12.6 mm) are doubtfully identified as 0. pectinata canalis. The ribs of another small La Boca valve, listed as Glycyneris sp., are somewhat angular.
 The lectotype is immature (length 14.6 mmn), at a growth stage preceding the appearance of minor secondary sculpture. Plate 81, figure 5, shows an imimahire left valve that has a very narrow space between primary ribs and a faint trace of an interstitial thread between some anterior ribs.
 The middle Miocene Clycyineris inl southeastern Costa Rica that has arched, instead of angular, ribs is accepted as G. pectiiiata canalis. Only a few immiature valves are in Rio l3anano ITSNM collections (ITSGS 5882g), 5882h). Typical mature shells are fouiid ]in middle Miocene deposits on the Pacific side of Panami. in Chiriqui Province (USGS 7.955). Despite unillustrated


records, it is doubtful whether the typical form occurs in Colombia and Venezuela. On the ventral part of the shell of G. canalis colombiensis (Weisbord, 1929, p. 11, pl. 2, figs. 3, 4) the ribs are separated by linear grooves.
 As recognized by Brown and Pilsbry, G. pectinata canalis is closely related to G. pectin ata pectin ata (Gmnelin), living in the Caribbean region. Many large specimens of the nominate subspecies show minor secondary sculpture like that of the fossils. The nominate subspecies, however, is somewhat smaller (maximum length 32 mm in USNM collections) ; in fact, most lots aire decidedly smaller. A very narrow space between ribs is the prevailing sculpture among living shells.
 Occurrence: La Boca formation (early Miocene; ideiitication doubtfull, localities 1 15,116a. Lower member of Aihajuela formation (early Miocene; identification douibtful), locality 82 (sp.), 82a. Middle and upper parts of Gatun. formation (middle Miocene). Middle part, eastern area, localities, 144d, 147b, 155,155~a, 155b; western area, localities 160, 160c. Upper part, eastern area, locality 1M73 Middle Miocene deposits, Lim6n Province, Costa Rica. Middle M\/iocenie deposits, Chiriqui Proviiice, Panamaii.
 Group of Glycymeris arotata
 A group of species typified by Clycymeris arciata (Conirad) (1848, p. 125, pl. 13, fig. 24; Oligocene, Mississippi) is unknown in southeastern United States later than early Miocene time. It is represented in the Tampa limestone, of that age, by G. lainyi (Dall, 1915, p. 122, pl. 20, figs. 11, 13; G. lamyi tavpae Mansfield, 1937, p. 190, pl. 10, figs. 4, 6, 7, is a synonym.) On the contrary, the group survived in the Caribbean region until late Miocene time, but left no descendants in western Atlantic or eastern Pacific waters.
 Glycymieris (Tucetona) secticostata schencki Nicol
 Plate 72, figure 1, plate 75, figures 6, 7
Glycyrneris seltencki Nicol, Jour. Paleontology, v. 21, p. 349, p1.
 50, figs. 1-6, 1947 (Miocene, Canal Zone).
 Moderately small, trigonal-ovate, umbonal area niarrow, its margins sloping. Height slightly less to slightly greater than length, posterior margin slightly extended. Umbo sculptured with 19 to 26 arched primary ribs of uniform width and spacing, or partly irregular in width and spacing. Ribs of about same widths as space between them, or narrower than space, exceptionally wider than space. At height of 4 to 12 mum, primary ribs split into two parts, eventually on large shells into three or four p~arts. At about same stage ais splitting of ribs, interstitial rib or thread appearing in space between primary ribs, eventually two or three. Interstitial rib exceptionally as wide as branches of primary ribs on main part of shell. One to five primary ribs adjoining upper margins


521