. Fresh-water biology. Freshwater biology. THE MOLLUSCA 1019 170 (171) Shell thin and delicate, suborbicular to oblong; beaks prominent, usually retaining the nepeonic valves; cardinal teeth minute, often obsolete; anterior and posterior laterals present. MiiscuUum This group has a general distribution. The prominent beaks with the distinctly mari^ed nepeonic shell are the distinctive feature, but in some species these are lacking. The thin, rounded, polished shell is, however, quite characteristic. , M. partumeium Say (Fig. Fig. 1530. 171 (172) Shell subrhomboidal, thin, modera
. Fresh-water biology. Freshwater biology. THE MOLLUSCA 1019 170 (171) Shell thin and delicate, suborbicular to oblong; beaks prominent, usually retaining the nepeonic valves; cardinal teeth minute, often obsolete; anterior and posterior laterals present. MiiscuUum This group has a general distribution. The prominent beaks with the distinctly mari^ed nepeonic shell are the distinctive feature, but in some species these are lacking. The thin, rounded, polished shell is, however, quite characteristic. , M. partumeium Say (Fig. Fig. 1530. 171 (172) Shell subrhomboidal, thin, moderately inflated, with the posterior side longer; cardinal teeth feeble, only one in each valve. Eupera Bourguignat. A tropical group, of which two or three species occur in Florida, Ala- bama, and The rhomboidal shape is characteristic. The shells appear to be mottled and are usually so described, but according to Dr. W. H. Dall these "spots" are caused by a parasitic infusorian that attacks the interior of the shell. Example, E. singlcyi Pils. (Fig. 1531; Fig. isji. 172 (169) Shell small, rounded, oval, or obliquely cuneiform, inequilateral, anterior side longer; beaks sub terminal; carchnal teeth double in each valve. Pisidium C. Pfeiffer. The Fisidia are of general distribution and a great number of species have been described. They arc easily distinguished from the allied genera by the very inequilateral shell, the hinge being on the shorter side. , P. virginkum Bgt. (Fig. 1532; X 2). Fig. IS3S- 173 (174) Shell rounded, inflated, thin; beaks forward; surface smooth or slightly concentrically sculptured; cardinal teeth, two in the right and one in the left valve; no lateral teeth. Family Cyrenellidae. Only one genus Cyrenella Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
