PISIDIUM. 115 



Pisidium variabile.* 



Cychis nitida, Mighels, Linsley, Amer. Jour, xlviii. 276 (1845). 

 Pinidium variabile. Prime, Bost. Proc. iv. 163 (1851). 

 Pisidium (jrande., Whittemore, in litt. 1855. 

 Muscidium vnriahile, Adams, Rec. Gen. ii. 452 (1858). 

 Pisuni variabile, Adams, loc. sup. cit ii. 660 (1858). 



Shell heavy, ol)li([nc, inequilateral, inflated ; anterior side longer, 

 narrower, somewhat angular at end ; poste- 

 rior subtruncate ; Ijeaks situated posteriorly, 

 full, prominent, not approximate at aiwx ; 

 valves solid, interior light hlue ; striaj regu- 

 lar, l)ut very distinct; epidermis glossy, very 

 variable, straw-color or greenish-brown with 

 a yellow zone on the basal margin ; hinge- 

 margin cu]-vcd ; hinge rather slight ; cardi- 

 nal teeth united, small ; lateral teeth dis- „ .... „ , 



' ' p. vnriahile. Enlarged. 



tinct, strong, short. Length, twenty-one 



hundredths of an inch ; breadth, eighteen hundredths of an inch ; 



width, seventeen hundredths of an inch. 



North America, in New England, and in the States of New York, 

 Pennsylvania, and Virginia. 



This species has hitherto always lieen looked upon ])y collectors 

 as the P. virg-inicNiii ; but having compared it with the original 

 shells, described as Ci/cJas dubia, Say, by Dr. Grould, in his Re])ort, 

 and with some sjjecimens of P. vir^micum from Westlield, Mas- 

 sachusetts, sent to me l)y Professor C. B. Adams, as well as Avith 

 some others sent to me from Philadelphia, l)y Professor S. S. Hal- 

 deman, I have become convinced that it is different from Say's 

 shell. Compared with the young of P. virg-itdcum, it is more ob- 

 lique, less elongated, more inflated, and of a different color. This 

 species is not so elongated as the P. virginicmm ; it 

 is more inflated, the beaks are larger and more tu- rig. 428. 



mid ; it is also a much smaller shell. Say describes 

 Cychis dnbia as being six twentieths of an inch in 

 length ; P. variabile is only four twentieths of an p. variabile. 



inch in length, and that it is a full-grown shell I 

 am led to believe, not only from its heavy striations and mature ap- 

 pearance in general, l)ut also from having found young in the shell. 

 The young is not so oblique as the adult ; it is more elongated, less 



* See note, page 107. 



