46 GEOLOGY AND PALEONI

"At Gatun, or Monkey Hill?, where we stopped for a few moments, I obtained several fossil shells from the embankment at the side of the road" (Blake, 1857, p. 1). He evidently meant he was not certain whether the place where the train stopped was Gatun or Monkey Hill, although that uncertainty seems strange. Two of the three species he collected (Lirophora mactropsis and Clementia dariena) are not known to occur at Monkey Hill [Mount Hope], whereas they do occur at Gatun. The preservation and matrix of the type of Lirophora mactropsis strongly suggests unit 1 of the section on page 44. There is no reasonable doubt that Blake picked up his fossils at Gatun. According to the locality data in Conrad's description of Newberry's fossils, Newberry on his trip two years after Blake's also collected at Gatun (Conrad, 1857a, p. 72). Conrad recorded five species, but Gabb added eight others, including the only cephalopod to be found in the Gatun formation (Gabb, 1881). Some of Newberry's fossils have been found recently at the Academy of Natural Sciences of Philadelphia.
 Other Gatun fossils of the same vintage were collected at Monkey Hill (Mount Hope of present terminology) in 1857 by J. Rowell. Some of Rowell's specimens have early Smithsonian Institution catalog numbers (63916395), which were entered in 1880 under the locality "Monkey Hill, near Gatun." Most of them, however, have National Museum catalog numbers entered in 1893 under the locality "near Gatun." One of the latter series of numbers has the notation "collected in 1857." It is assumed that "near Gatun" should read "Monkey Hill, near Gatun." According to Dall, Rev. J. Rowell was an old collaborator of the Smithsonian Institution and a pioneer of 1849 in California (Guppy and Dall, 1896, p. 307). Rowell also collected fossils in the Dominican Republic. Unfortunately some of his specimens, including the types of Phos metuloides, Terebra bipartita spirifera, and Pecten scissuratus, are alleged to be from the Dominican Republic, but evidently were collected at Mount Hope. On the contrary, a few labeled "near Gatun" apparently were collected in the Dominican Republic.
 The bulk of the collections at the National Museum was gathered during the period 1911-13 by MacDonald and Vaughan. Notable later accessions resulted from the field work of Olsson and other geologists of the Sinclair Central American Oil Corporation in 1918. The most recent collections studied for the present report are Thompson's made in 1942-43 and my own resulting from the 1947 field work for the present report.


0


LOGY OF CANAL ZONE

 A total of 90 collections is being studied for the present report: 9 from the lower part of the formation, 58 from the middle part, and 23 from the upper part. On the basis of slight faunal differentiation, the collections from the middle part are divided into those from* an eastern area (east of the canal, 43 collections) and, those from a western area (west of the canal and west of Gatun Lake, 15 collections). On the basis of both: faunal and age differentiation, an eastern area in the Canal Zone (15 collections) and a western area, comprising the western coastal district (8 collections), are recognized in the outcrop area of the upper part. As shown by the data in the description of localities (p. 125-129), many collections, particularly from the" middle part of the formation in the eastern area, are, duplicates or virtual duplicates. Three collections contain more than 100 species: those from localities138a and 155 (both about 125 species), and locality 147b (about 110 species). The first two are among Thompson's collections from the lower and middle parts of the formation, respectively. The third, one of MacDonald and Vaughan's from the middle part, is especially rich in minute specimens, including 300 or', more of Teinostoma spermatia and about 200 microscopic shell tips of Turritella altilira.
 The scattered publications describing mollusks of theGatun formation are listed on pages 5-10. The most important are those by Toula (1909, 1911), Brown and Pilsbry (1911, 1913), and Olsson (1922). Almost allthe large species that occur in the middle part of theformation have been described, but most of the minute species in that part, and many of both large and minute species in the lower and upper parts are described for the first time in the present report.
 The available molluscan fauna is estimated to totalabout 350 species. In chapter A of the present report 46 species and subspecies are described and 4 others, not represented in the collections at hand, are recorded. The species included in chapter A are tabulated on page. 48. In that table "cf." in the locality columns indicates the presence of incomplete or poorly preserved materials that may or may not represent the form listed opposite in the species column. Likewise the designation "sp." in the locality columns means an unidentified incomplete or poorly preserved species that may or may not be the same as that in the species column. The designation "?sp." in the locality columns indicates thatthe genus is questioned. The columns labeled "Other. collections" list species or occurrences not represented in the collections at hand.