MAZATLAN BIVALVES ty 
striz are coarser and more irregular. This (posterior) portion 
of the shell is covered with very copious epidermis, in wrinkled. 
folds, as in Saxicava rugosa. Ligament long. The young shell 
has projecting umbos, and often serrated edges to the anterior 
gape. The largest specimen measures long. 57, Jat.1°17, alt. 57. 
The smallest valve, long. ‘02, lat. °05. 
Hab.—In Spondyli, Isle of Perico, Panama, Cuming.— Mazat- 
lan; not uncommon in Spondylus Lamarcki, very rare in 
Chame, Patella Mexicana, and in Imperator olivaceus and 
unguis ; L’pool & Havre Coll.* , 
Tablet 43 contains 6 valves very young, and 3 pairs adolescent. 
44, Young specimen, piercing the apex of Imperator unguis. 
45, do. Imp. olivaceus, with Bryozoa, &c. attached.—46. Young 
specimen in situ in Imp. olivaceus, with another younger, coter- 
minal.—47. Young specimen in Imp. olivaceus, with tube some- 
what projecting, which is unusual at Mazatlan.—48. I. olivaceus 
broken across, and shewing 5 specimens of G. truncata, and 
one Lithodomus caudigerus, invading the Imperator’s liver 
chamber. —49. Adolescent specimen in situ in fragment of 
Spondylus, with the tube laid bare, and the pedal chink and 
deposit. Also portions of several other tubes of Gastrochena, 
Lithodomus and Petricola.—50, 3 adult specimens varying in 
outline, of which one displays a pearl formed near the hinge, 
another a lamina cutting off a large part of the anterior end, as 
often happens in large aged fossil Saxicave.—5l. Fragment 
of Spondylus, displaying hole of G. truncata, which, having 
approached a Lithodomus too closely, has turned round, filling 
the vacant space with shelly matter.—52. Siphon pipe laid bare, 
by the decay of the worm-eaten Spondylus around: also bur- 
rows of Lithodomus plumula and Parapholas calva.—3, Pipes 
and thick lining of 3 Gastrochene in Patella Mexicana: the 
two siphons in one are ail-but separated at the extremity.— 
54, 2 pipe-ends from Spondylus.—55, Fragments of shelly lining. 
22. GASTROCHENA OVATA, Sow, 
Proc. Zool. Soc. 1834, p. 21. 
Burrow not differing perceptibly from that of G. truncata. 
Shell, when fresh, of a delicate lilac tinge, with sharp elegantly 
bent concentric ridges following the margin, closer at the an- 
* In the Bristol Institution is a Tablet marked G. cuneiformis, from the West 
Indies, Mr. Priske, containing 2 specimens ; of which one I was unable to separ- 
ate from G. ovata, the other (in its burrow) from G. truncata. Mr. Hanley 
states, from the examination of a collection made by M. Bean in Guadaloupe, 
ra sent to him by M, Petit, that several species of borers are common to the 
wo oceans. 
