126 MAAZTLAN BIVALVES 



is tlie pattern constant, tliougli there is a general adherence to 

 a particular plan. It often presents the appearance of grains 

 of detritus cemented together by animal matter, these grains 

 also covering the body of the shell much more coarsely than 

 in L. aristatus. It is thus that the young shells can generally 

 be separated ; the epidermal tubercles being much larger, and 

 the concentric wrinkles stronger. The number of specimens 

 however was not large enough to ascertain these points with 

 precision. The differences in the pattern of incrustation do 

 not accompany those in form. The shape presents the same 

 two extreme varieties, gracdior and tumidior, as inL. aristatus. 

 The parallelism of the margins also is not constant. The bur- 

 rows are in most respects like those of L. aristatus, g. v. They 

 are shaped like the shell, and aUow very little space for the 

 opening of the valves. The orifice is almost close to the ex- 

 terior, and is not bdobed. The largest perfect specimen 

 measures loncf. 1'86, lat. '53, alt. '5. A very tumid sp. in 

 Mr. Darbishire's Col. measures long. 1"9, lat. '9, alt. '6. 

 JIab. — Panama, in Spondyli, Cuming. — Philippines [?], Han- 

 ley. — Mazatlan ; rare in Spondyli, very rare in Chamse and 

 Patella Mexicaua ; IL'pool ^' Havre Col. 

 Tablet 572 contains 6 pairs young, the smallest '08 in 

 length.— 573, 4 sp. adolescent and adidt, typical fonn. — 574, a 

 sp. in situ, burrowing in the attached part of the Spond^ylus 

 calcifer : portions of the rock remain, which appear to have 

 been bored by Pholads ; a burrow is seen of P. calva. — 575, 

 2 fragments shewing the extremities of the burrows which are 

 more nearly round than in L. aristatus. — 576, fragments illus- 

 trating shell structure. — 577, do. incrustations. 



Tablet 578 contains 3 sp. different ages, var. gracilior. 

 Tablet 579 contains 1 pair and 2 valves do., var. tumidior. 

 Tablet 580 contains ^. sp. with the anterior part less swollen, 

 and the lines not parallel. 



176. LiTHOPHAGUS ABISTATUS, Sol. 



Mvtilus aristatus, Dillic. Descr. Cat. 1817, vol. i. p. 303, no. 8.— 



'Solancler, ms..— Wood, Lid. Test. pi. 12, f. 8. 

 Lithodomus aristatus, Forbes Sf Hani. Br. Moll. vol. ii. p. 212. 

 Enc. Mail. Vers, pi. 221, f. 8, a, b. 

 Le Ropan, Adans. Sen. p. 267, pi. 19, f. 2. 

 Mvtilus litho])hagus striatus, J. Sow. Linn. Trans. 1804., 



vol. viii. p. 271, pi. 6, f. 2, 3-5. 



