273 



size, by its smooth and polished surface. Compared to C. cor- 

 nea, it is less globose, laterally more angular, the beaks are 

 rather more tumid, but less rounded ; lastly, it is more solid and 

 differently colored. 



This shell seems, as yet, to be but very little known ; besides 

 the specimen I possess, I have seen but one other, which was 

 kindly sent to me for description by Prof. C. B. Adams. 



3. CYCLAS FABALIS Nobis. Bost. S. N. H. Proc. iv. 159. 

 Cabinet of the B. S. N. H. 



Shell. Vide Bost. S. N. H. Proc. iv. 159. 



Localities. Lake Superior, (Agassiz.) Tennessee, (Budd.) 



The only species to which this shell is allied is the C. cas- 



tanea ; it differs, however, in being less inflated, the posterior 



margin is more abrupt, and the beaks are not quite as depressed ; 



the coloring and size are not only different, but it is also more 



elongated. 



4. CYCLAS CASTANEA Nobis. Bost. S. N. H. Proc. iv. 160. 

 Cabinet of the B. S. N. H. 



Animal. Siphons of a medium size. Color crimson-red. 



Shell \ r ide Bost. S. N. H. Proc. iv. 160. 



Localities. Wabash River, (Haldeman.) Ohio, (Anthony.) 

 Osvasca L. (Redfield.) Tenn. (Budd.) Greenwich, N. Y. 

 (Ingalls.) Chuck River, Virginia, (Anthony.) 



Shell very rare. I have found it at the roots of plants in com- 

 pany with P. compressum, P. dubium, and P. variabile. The 

 animal, when in confinement, I have observed to exhibit con- 

 siderable activity. 



5. CYCLAS DETRUNCATA Nobis. Bost. S. N. E. Proc. iv. 155. 

 Cabinet of T. Prime. 



Shell. See Bost. S. N. H. Proc. iv. 155. 

 Locality. Schuylkill River, (Richard.) 



This shell is remarkable for the sudden narrowness to which 

 its anterior extremity is brought. 



PROCEEDINGS B. S. N. H. 18 APRIL, 1853. 



