MAZATLAN BIVALVES 131 



the cell, leaving it of a produced ovoid. It is large enough to 

 allow of considerable expansion and revolution of the shell 

 within : but so far from showing marks of friction, the internal 

 coating of both cell and pipe are very glossy. The deposit 

 is sometimes ' 4 thick. 



The animal is gregarious: ten burrows having been found 

 in one Spondylus valve, of which six appeared of more recent 

 date than the rest, being carried across the others. One 

 of these, in crossing a burrow of its predecessor, had obliterated 

 one half of the valves of the dead shell, and built-in the remain- 

 ing portion with the wall of the new cell ; another had cut 

 across and cemented a Cumingia in the same way. 



The shell is short, bent, scarcely angled at the dorsal margin, 

 well rounded at the ends, and slightly excurved in front. The 

 hinge line is very long, with the usual sharp ridge within. It 

 is not sufficiently fresh to display the muscular impressions 

 distinctly. There are no proj ecting incrustations ; the deposit 

 being thin and equally diffused. The shape of the shell is not 

 such as would have been predicated from the form of its habi- 

 tation ; which had given rise to many surmises, before the 

 shell now described was found entombed, without possibility of 

 error. This shell, which is somewhat young, measures long. 1 *5, 

 lat. '55, alt. '47 ; its cell is *65 across. The largest cell measures 

 long. 3*26, lat. 1*2: its tube, long. 1*6, lat. (in the middle) '3, 

 alt. '2. 



Hob. Mazatlan ; extremelv rare, in attached valves of Spon- 

 dylus calcifer ; L'pool Col. 



Tablet 605 contains a young shell '06 in length, which may 

 belong to this species, though its affiliation cannot be deter- 

 mined without a series. It may possibly be a young L. cin- 

 namomeus. Also a fragment of a large shell. 606, Spondylus 

 valve, containing the two largest burrows, unfortunately broken 

 in obtaining a cast : also burrows of Gastroch&na truncata, &c. 



179. LEIOSOLEJTUS , sp. ind. 



One specimen was found by Mr. Darbishire, differing from 

 the rest in the following particulars. Shell much shorter, 

 broader, and with the hinge line and dorsal margin at a much 

 smaller angle. Cell not so smooth, with dark gray walls, 

 scarcely polished. Pipe emerging without any contraction, 

 but with a raised ridge within the cell. The shell being very 

 much decomposed was unfortunately broken to pieces in 

 extraction. 



