Chap. 6. 



INVERTEBRAL ANLMALS OF VERMONT. 



1G5 



FRESH WATER AND I.AM) SHELLS. 



straight, rising into n. wing posteriorly ; 

 j)osterior margin very obliquely descend- 

 ing to a truncate extremity ; inferior mar- 

 gin nearly straight; anterior margin reg- 

 ularly rounded ; interior surface bluish, 

 iridescent. Length 2.4 inches, height 1.2-") 

 inch, width 0.9 inch. 



Rejiarks. — A few small specimens of 

 this species have been found in Middle- 

 bury. In Massachusetts and further soutli 

 it attains a mucli greater size. It is very 

 similar to the preceding, but is distin- 

 guished by its wing, small beaks, and 

 convex disc. It more nearly resembles 

 Jl. cygiica of Europe. 



Jinodonla undulata. — Say. 



Description. — Shell oblong ovate, wi- 

 dest behind the beaks, not thin, with 

 coarse and fine stria; of growth ; e])ider- 

 mis yellowish, brownish, or blackish 

 green, with numerous irreoular dark 

 green rays, which are obscured when the 

 general color is dark; beaks quite prom- 

 inent, much undulated ; discs moderately 

 inflated, convex ; anterior side usually 

 less, sometimes more than one third as 

 long as the posterior ; hinge margin near- 

 ly straight ; posterior margin descending 

 in a curve through a third of the length 

 ^fthe shell, then abruptly- rounded into 

 the inferior, which is slightly curved or 

 straight ; anterior margin regularly roun- 

 ded ; interior bluish, but often covered 

 with a light salmon colored nacre, with a 

 dark blue or brown margin; hinge with 

 obsolete teeth. Dimensionsof two speci- 

 mens : No. I, length 2.75 inches, height 

 1.4 inch, width 0.d5 inch. No. 2, length 

 2.65 inches, height 1.45 inch, width 1.1 

 inch. 



Remarks. — This species is found in 

 small streams and in lake Champlain. — 

 -When the epidermis is of a light color and 

 the rays conspicuous, it is a very beauti- 

 ful shell. More frequently it is dark, and 

 the appearance unattractive. It is inter- 

 mediate between this genus and the next. 



Ge.n'us Alasmodonta. 



Generic Chan-acters. — SI, ell as in Anoilonta. 



but furnished uitli a sloiit, slriated, and simple 



or divided cardinal tooth in each vaK-e ; also the 



shell is usually thicker. Anitnal as in Aiiodoiita. 



Alasmodonta arcuata. — Barnes. 

 Description. — Shell very long ovate, 

 arcuate ; epidermis black, or browni.sli 



black, with very distinct striae of growth, 

 very much developed at the margin ; 

 beaks small, depressed, much eroded ; 

 discs moderately inflated, flattened; an- 

 terior sides more than one-fourth as long 

 as the posterior; hinge margin regularly 

 curved into the posterior, which descends 

 at first very obliquely, and is then irregu- 

 larly rounded into the basal margin; this 

 is incurved, and the anterior is regularly 

 rounded ; interior with a brilliant, thick 

 nacre, iridescent posteriorly. Length 4.9 

 inches; height 2.2 inches; width 1.35 

 inch. 



REMARKS.-This species has been found 

 at Burlington. It has been considered 

 identical with L'nio margariti.ferus of Eu- 

 rope, but that shell is shorter, and has the 

 beaks more central and elevated. It yet 

 more nearly resembles the Inio simuitiis 

 of Europe, which is higher and has the 

 beaks more central. Perhaps it may not 

 be distinct from the latter. The young 

 have the basal margin straight. It is 

 found throughout New England. 



Alasmodonta riigosa. — Barnes. 



Description. — Shell ovate ; epidermis 

 with irregular incremental stria?, which 

 are mostly fine, greenish brown ; beaks 

 small, not prominent, undulate ; discs 

 flattened, with two ridges extendino- pos- 

 teriorly in slightly curved lines, between 

 and above which the surface is. crowded 

 with numerous crowded wrinkles, which, 

 for the most part, run posteriorly and up- 

 wards ; anterior side much depressed, 

 about one-third as long as the posterior ; 

 hinge margin arcuate behind the teeth, 

 otherwise nearly straight, ascending pos- 

 teriorly ; posterior margin descendino- in 

 a straight line to the upper umbonial an- 

 gle ; extremity truncate between the um- 

 bonial angles ; inferior margin nearly 

 straight ; anterior margin regularly round- 

 ed ; inner surface often with a light sal- 

 mon-colored deposit. Length 4.1 inches; 

 height 2.3 inches; width 1.25 inch. 



Rk.marks. — This species is common in 

 the western states, where it attains a 

 greater size. Lake Champlain and the 

 streams west of the Green Mountains ap- 

 pear to be the most eastern limit of its 

 habitation. 



Alasmodonta undulata. — Sa y. 

 Description. — Shell ovate, epidermis 

 smooth, blackish or greenish brown, with 

 obscure darker rays; beaks large and 

 prominent, with large and deep undula- 

 tions ; discs much inflated and convex, 

 with a ridge more or less obtuse extend- 

 ing posteriorly ; anterior side small, one- 

 sixth to one-third as long as the posterior ; 

 hinge margin sinuous or simply curved ; 



