130 MAZATLAN BIVALVES 
tremely rare, burrowing in Chama; L’pool Col.—Fossil, 
near Rome, Lamarck. 
Tablet 604 contains the remains of the valve. 
Sus-cenus LEIOSOLENUS. 
Animal profunde in matricem penetrans, cameram capacem, 
politam excavans, partem derelictam explens preter tubum 
Levem partim bilobatum, ? siphones longos tenentem. Testa 
Lithophago similis. 
If the animal, when examined, proves to have long, excur- 
rent siphons, it must take generic rank perhaps in the neigh- 
bourhood of Mytilimeria, Conr. 
178. LEIOSOLENUS SPATIOSUS, 2. S. 
S. t. dactyliformi, tenuissimd, curtiori ; postice concentrice 
undulata; umbonibus celatis; inerustatione calearid, tenui, 
equaliter totam superficiem tegente, plerumque pustulis trans- 
verse confluentibus munita ; marginibus antice et postice rotun- 
datis, ventraliter subexcurvatis; lined cardinali prelonga, 
margine dorsali curvato, subangulato, curtissimo. Camera 
obovali, spatiosa, nitidissimd : tubo nitido plus minusve elongato, 
juxta cameram contracto, postice bilobato. 
Several chambers of this remarkable shell were found by 
Mr. Darbishire ; always in the lower valves of Spondylus, and 
generally open as if part of the burrow were excavated in the 
rock. This may account for the loss of the shells except in a 
single instance. In the largest specimen, presented by him to 
the Br. Mus., are seen two chambers, which, from the long 
bilobed pipe of one of them, might be taken for the work of 
an enormous Gastrochena. The pipes are however perfectly 
smooth within, while in Gastrochena they are corrugated. The 
bilobation is only at the extremities, the rest of the pipe being 
irregularly circular, and much contracted at its junction with 
the cell. As there is no evidence of pallial sinus in the shell 
(though it may possibly exist.) it is probable that the con- 
traction of the siphons takes place outside the body of the 
animal, Krom an examination of a specimen broken in the 
line of axis of the cell and pipe, it appears that the creature 
begins life with the shortest possible tube and a somewhat 
conical cell: as it burrows deeper, it not only fills up the cor- 
responding posterior space with concentric layers of shelly 
deposit, pierced by the pipe; but also proportionally shortens 
