118 MAZATLAN BIVALVES 



GENUS MYT1LUS, Linn. 



167. MYTILUS PALLIOPUNCTATUS, DJcr. 



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

 varie detritd ; rugis incrementi concentricis scepe instructd ; 

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

 tenuissime aratd, plus minusve indutd ; margine dorsali et car- 

 dinali parum excurvato ; ligamento solido, extus umbones spira- 

 liter ascendente ; pagind internd pulcherrime atro-purpured, 

 splendente, apertiiram bi/ssalem versus pallidd, punctis 

 sparsim valde i mp ressis ; cicatricibus muscularibus conspi- 

 cuis, plerumque maxime corrugatis. 



M. tenuiaratus, Dlcr. ins., a prima manu. 



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

 rubbed at various angles, but when perfect exhibiting very 

 fine radiating striulae, 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 surface, 

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

 observed displaying the umbos distinctly, 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 striulse nor punctures, and are scarcely 

 to be distinguished from the smooth variety of the next species. 

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

 Hab. Mazatlan; abundant, but always rubbed; L'pool # 



Havre. Coll.S. W. Mexico, P. P. C. 



Tablet 528 contains 7 sp., very young, the smallest '04 

 across. 529, a sp. with numerous young 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. 536, 3 do. distorted growth. 537, 2 do. mantle cleft. 

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



168. MYTILUS MULTIFOEMIS, n. s. 



M. t. parvd, maxime variante, sed plerumque angustd, 

 prope cardinem tumidd, angulo perobscuro diagonali ; marqine 



