118 MAZATLAiJ BIVALVES 



Genus MYTILUS, Linn. 



1(>7. MyTILUS PALLIOrXJNCTATCS, Dkr. 



M. t. subrectd, elongatd, angustd, tumidiore, solida, plerumque 

 vane detritd ; ritgis incretnenti concent rid s S(ppe instructd ; 

 epidermide crassd, corned, fusco-olivaced, horridiore, radiatim 

 tenuissime aratd, plus minicsve indiitd ; margine dorsali et car- 

 dinali pamm excm'vato ; ligamento solido, extiis umhones spira- 

 liter ascendente ; pagind interna pulchennme atro-purpured, 

 ■splendente, apei-tiiram hyssalem versus pallidd, punctis 

 sparsim valde i mp r i s s i s ; cicatricibus mu^cularibus conspi- 

 cuis, plerumque maxime corrugatis. 



M. tenuiaratus, Dkr. ms., a prima manu. 



Shell long, swollen, rather straight, pointed, almost always 

 rubbed at various angles, but when perfect exhibiting very 

 fine radiating striul?e. and sometimes much stronger concentric 

 lines of growth. Interior of a lustrous dark purple, white near 

 the byssus, punctured over the principal part of the siirfacc, 

 as in many species of Semele. In the only adult specimen 

 observed displaying the umbos distinctlj', the ligament is seen 

 to wind towards them outside the shell, presenting an appear- 

 ance as in some Myoconchse. The muscular impressions are 

 strongly marked, and often very rugose. The very young 

 shells display neither striula? nor punctures, and are scarcely 

 to be distinguished from the smooth varietj* of the next species. 

 Long. 3 5, lat. 1'38, alt. 1"3. 



Hah. — Mazatlan ; abimdant, but alwavs rubbed ; L'pool Sf 

 Havre. Coll.—S. W. Mexico, P. P. C. 



Tablet 528 contains 7 sp., very young, the smallest "Ol 

 across. — 529, a sp. with numerous joung outside, in situ. — 

 530, 8 pairs and a valve of successive ages, normal form. — 531, 

 5 do. elongated. — 532, 5 do. very narrow, elongated.— 533, 5 sp. 

 curiously rubbed. — 534, 1 do. with one beak "26 shorter than 

 the other. — 535, 1 do. persecuted by Lithophagi about the 

 hinge. — 53(5, 3 do. distorted growth. — 537, 2 do. mantle cleft.— 

 538, 4 sp. jun. shewing interior. — 539, 4 do. adult. 



168. Mttilus multifobmis, n. s. 



M. t. p a r V d, maxime variante, sed plerumque angustd, 

 prope cardinem tumidd, angulo perobscuro diagonali ; margine 



