IIACII.ERA. 45 



removed. Epidermis straw-colored, or becoming fawn-colored, 



sliixlitly wrinkled posteriorly. Within 



livid, smooth, and slnnnig, lieconnng 



thickened l)y age. Tlie red stripe is 



visible within, and covered by a faint, 



rib-like thickening. 



Hinge of two large, ascending teeth s.dn-hus. 



on eacli valve, one of which, on the 



left valve, grows broad, and is emarginate at tip. Length, one and 

 one half inches ; height, one half inch ; width, seven twentieths of 

 an inch. 



Tliis, like the preceding species, is occasionally found at New 

 Bedford, and other places in Buzzard's Bay. It is rather common 

 about Rhode Island. I have never met with a specimen north of 

 Cape Cod, though if our shell be identical with the S. frag-i/is of 

 British writers, it is found on the Canada coasts. It differs from 

 the fragile specimens known in British cabinets, simply in growing 

 to a much larger size, and becoming quite thick and strong. 



Genus MACH.EKA, Gould. 1841. 



Shell oblong-oval, compressed, inequipartite, moderately gaping ; 

 beaks minute. Hinge with three diverging cardinal teeth in tlie 

 left valve, the middle one bifid, the third one compressed, delicate, 

 taking the direction of the margin, or obsolete ; on the right valve 

 two teeth, entering between those of the opposite valve. Within, 

 usually crossed by a strong, vertical rib. Muscular impressions 

 joined by a deeply sinuous pallial line. Ligament prominent. 



Animal not much larger than the shell ; lobes of the mantle 

 united for al)out half their length, the whole of their margin pecti- 

 nated with fleshy teeth, from near the siphon to the hinge, except 

 where they pass over the foot ; similar Ijodies are also found along 

 their inner sub-margin, near the siphon. Labial palpi long, extend- 

 ing quite across the foot, pointed. Branchiae extending to the open- 

 ing of the siphon and embracing about half the breadth of the foot. 

 Foot hatchet-shaped, dilating towards its extremity, which is ob- 

 liquely truncated. Siphons united to their tips, wdiich have scat- 

 tered hairs. 



The above is the description of the animal of M. costala. It dif- 

 fers from Dcshayes's description of the animal of Solecurtus stngil- 



