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 sufliciently fresh to display the muscular impressions 
distinctly. There are no projecting 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 hahi- 
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 /ong. 1°5, 
lat. °55, alt. °47 ; its cell is ‘65 across. The largest cell measures 
long. 3°26, lat. 1‘2: its tube, Zong. 1°6, dat. (in the middle) °3, 
Bl tana: 
Hab.—Mazatian ; extremely rare, in attached valves of Spon- 
dylus caleifer ; Z’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 Gastrochena truncata, &e. 
179. Le1osoLENus —— » 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. 
