130 MAZATLAN BIVALVES 



tremely rare, burrowing in Chama; L'pool Col. Fossil, 



near Rome, Lamarck. 



Tablet 604 contains the remains of the valve. 



SUB-GENUS LEIOSOLENTJS. 



Animal profunde in matricem penctrans, earner am capacem, 

 politam excavans, partem derelictam explens prceter iubum 

 Ice vein partim bilobatum, ? sipkones longos tenentem. Testa 

 LithopJiago 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. LEIOSOLEXUS SPATIOSUS, n. s. 



S. t. dactyliformi) tenuissimd, curtiori ; postice concentrice 

 undulatd ; iimhonibus celatis ; incrustatione calcarid, tenui, 

 cegualiter totam superficiem tegente, plerumque pustulis trans- 

 verse conjluentibus munitd ; marginibus antice et postice rotun- 

 datis, ventraliter subexcurvatis ; lined cardinali pr&longd., 

 tnargine dorsali curvato, subangulato, curtissimo. Camera 

 obovali, spatiosd, nitidissimd : tiibo nitidoplus minusve elongate, 

 juxta cameram contracto, postice bilol'ato. 



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 G-astrochsena. The pipes are however perfectly 

 smooth within, while in G-astrochama they are corrugated. The 

 biiobation is only at the extremities, the rest of the pipe being 

 irregularly circular, and much contracted at its .function 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. From 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 j but also proportionally shortens 



