163 



more elevated ; the color is also different. Found very rarely at 

 Fresh Pond, near Cambridge, in the spring. 



PisiDiuM RUBELLUM. P. tcsta minuta, compressa, subelon- 

 gata, alba, nitida, tenui, postice subtruncata, tenuiter striata, 

 umbonibus magnis, complanatis, elevatis. Long. 0.17 ; lat. 0.14 ; 

 diam. 0.10 inches. Hob. Lake Superior. (Agassiz.) 



Shell small, fragile, compressed, somewhat elongated ; stria- 

 tions very fine ; color light yellow. 



Remarks. This species is somewhat similar to the C. minor 

 of Adams, but is much more depressed and elongated, the beaks 

 are more prominent. Boston Society of Natural History. 



PisiDiuM VARIABILE. P. tcsta minuta, subovata, tumida, obli- 

 qua, triangulari, postice brevi et subtruncata, striis concentricis 

 iiistructa, umbonibus magnis, elevatis non approximatis, margini- 

 bus abruptis. Long. 0.21 ; lat. 0.18 ; diam. 0.179 inches. 

 Hah. Massachusetts. 



Shell small, stout and heavy, very oblique, rather inflated than 

 otherwise, posteriorly subtruncated ; beaks large, prominent, 

 but not approximate, margins rather abrupt ; color dark olive 

 green, generally with a zone of yellow on the margins ; stria- 

 tions rather heavy for so small a shell. 



Remarks. This species has hitherto always been looked 

 upon, by collectors, as the P. duhium, but having compared it 

 with the original shells described, as C. duhia, by Dr. Gould and 

 with some C. dubia, from Westfield, Mass., sent to me by Prof. 

 C. B. Adams, as well as with some other specimens sent to me 

 from Philadelphia, by Prof. S. S. Haldeman, I have come to the 

 conclusion that it is an undescribed species. 



This species is not so elongated as the P. duhium ; it is more 

 inflated, and the beaks are larger and more tumid ; it is also a 

 smaller shell than the P. duhium. Say describes the C. duhia 

 as being ^"^ of an inch in length ; the P. variahile is not that by 

 any means, and that it is a full grown shell, I presume by its 

 general appearance. Compared to the C. nitida of Adams, it is 

 much smaller and very much more inflated. 



This species varies very much in the scale from the younger 

 to the full grown ones, and I have thought the name of P. vari- 

 ahile would not be inappropriate. Found very abundantly in 



