MORSE: OBSERVATIONS ON LAMELLIBRANCHS. 
193 
protoconch is nearly circular, translucent and tumid, and 
curiously varies in size in different individuals. The line of imbri- 
cations along the posterior dorsal edge of the shell and the row 
running obliquely down to the lower posterior edge of the shell 
begin to form a short distance from the edge of the protoconch. 
Fio. 45. — Saxicava rugosa Lamarck. 
In a young specimen, fourteen millimeters long, a gelatinous 
thickening of the mantle protrudes from the posterior end en- 
closing the base of the syphons; this was spotted with brown and 
was observed in only one specimen. The creature was not 
timid. As in the case of other moUusks washed by the waves 
the animal may be handled without its contracting. At Mount 
Desert, Maine, the species was ovulating from June 4 to June 19. 
PHOLAS TRUNCATA Say. 
Fig. 46. Length, 54 mm. 
In Stimpson's Shells of New England, this species is recorded 
south of Cape Cod only, at New Bedford and in Connecticut. A 
few years ago it was found in Salem Harbor and I dug it at low 
tide in hard blue clay. The syphons are united, the branchial 
syphon wider in diameter than the anal. They extend over 
