BULLETIN FLORIDA STATE MUSEUM


 Richmond, Salmon River (MCZ 248075); Bay of Quinte, Adolphustown (ANSP 234653); BiUCE
 Co.: Pond nr. South Hampton (FMNH 130428); CANTWELL Co.: stream, Mono Mills (UMMZ
 133232); HASTINGS Co.: Hungerford, Dry Lake (MCZ 248101); Huntingdon, Moira Lake (MCZ
 248115); HAMILTON Co.: (ANSP 67569); Lake Simcoe (UMMZ 120625); Lake Huron, Cohome,
 Georgian Bay (ANSP 105668) Giants Tomb. Id., Georgian Bay (ANSP 105667); Cohome,
 Georgian Bay (ANSP 105744); Lake Huron, Gravelly Point, St. Joseph's Id., North Channel
 (ANSP 153108); LAMBTON Co.: Lake Huron, Kettle Point (UMMZ 133273); Manitou Island,
 s.e. side of Lake Mendemoa (UMMZ 52633); PRINCE EDWARD Co.: Lake Ontario (UMMZ
 138771); Athol Twp., Lake Ontario, Athol Bay (MCZ 248034); Matheson, Black River (MCZ
 248047). Rochester, Lake Ontario (CNHM 121181); TRONTENAC Co.: Kingston (MCZ 244222);
 Wellington, w. Lake, Ontario, Shore 300 yds. w. of Harbour Pier, Wellington (USNM 464527).
 PENNSYLVANIA. ERIE Co.: Presque Isle, Long Pond (CM 62.24729); Presque Isle, Middle
 Bend (CM 62.24731); Presque Isle, sand flats (CM 62.24728). VIRGINIA. Nr. Alexandria (CM).
 WISCONSIN. DANE Co.: Madison (FMNH 115418); Lake Mendota (CM 62.26283); DooR Co.:
 Newport, Newport Beach (FMNH 157444); MARINETTE Co.: North Woque Bay (UMMZ 120612);
 MILWAUKEE Co.: Milwaukee (USNM 7 lots); VILAS Co.: Rest Lake (FMNH 25727).
 REMARKs.-This snail has a wide geographic distribution within the cool
 temperate areas of North America's Great Lakes region. Within its range it
 occupies a wide variety of habitats, including lakes, ponds, marshes, rivers,
 and small streams. Most specimens that I examined came from habitats that
 were characterized by clear water with submerged aquatic plants. Though it
 is widely distributed, it is not known from geologic deposits older than the
 Wisconsin Glacial Period, nor from fossil localities outside its present range
 (Taylor 1960).
 Marstonia lustrica appears to be a species that originated in the upper
 Mississippi River system during the Wisconsin Glacial Period as a cold-
 tolerant member of Marstonia. It apparently moved north with the receding
 glacier, where it came to be widely distributed throughout the Great Lakes
 region.

 Marstonia halcyon new species
 DIA(;NOsis.-This species is distinguished by a small, broadly ovate shell with a deep suture
producing strongly shouldered whorls, a flattened periphery on the whorls, a wide umbilicus,
and complete peristome that is nearly uniformly thick. The suture descends to the aperture in
lateral profile. M. halcyon is related to M. castor and M. agarhecta, based on its slender apical
lobe on the verge with a small apical gland on the mesad surface of the tip and an enlarged penis.
It also shares with M. castor a small raised tubercular gland on the mesad surface of the verge,
but differs in this regard from M. agarhecta, which has only the apical gland.
 In addition to the characteristics of the verge, this snail differs from AM. lustrica and its allies
in having a slender copulatory bursa that does not extend to the end of the posterior pallial ovi-
duct and is nearly completely imbedded in glandular tissue.
 SHELL (FIGS. 3D, 17A-E). -The shell is small, usually less than 2.5 mm long, and is broadly
ovate in shape, being about 0.70-0.80 times as wide as high. The spire is as long as, or longer than
the aperture and is slightly convex in outline. The aperture is about 0.40-0.50 times the length
of the shell. The shell wall is nearly of uniformly moderate thickness and is almost transparent.
Specimens with a complete peristome usually develop a slight callused ridge within the peri-
stome. The periostracum is a very delicate light gray in color. The umbilicus is rather broadly
perforate. The whorls are densely sculptured, with fine irregular incremental striations that are
crossed by much finer spiral striations. There are about 4.0-4.3 whorls at maturity (4.3 in holo-
type); large gerontic specimens may have as many as 5.0 whorls. The suture is deeply impressed,
causing the whorls to be almost flat-topped and shouldered. The periphery of the whorls are dis-
tinctly flattened, with the apical whorl protruding above the succeeding whorls. The body whorl


Vol. 21, No. 3