118 MAZATLAN BIVALVES 
Genus MYTILUS, Lunn. 
167. Mytinus pattiopunctatus, Dkr. 
M. t. subrecti, elongata, angustd, tumidiore, solidd, plerumque 
varie detrita ; rugis incrementi concentricis sepe instructé ; 
epiderimide crassi, corned, fusco-olivaced, horridiore, radiatim 
tenuissime arata, plus minusve indutd ; margine dorsali et car- 
dinali parum excurvato ; ligamento solido, extus umbones spira- 
liter ascendenie ; pagind internd pulcherrime atro-purpured, 
splendente, aperturam byssal@m versus pallidd, punctis 
sparsim valde impressis; cicatricibus muscularibus conspi- 
cuis, pleruinque maxime corrugatis. 
WW. tenuiaratus, Dkr. ms., a prima manu. 
Sheil long, swollen, rather straight, pointed, almost always 
rubbed at various angles, but when perfect exhibiting very 
fine radiating striule, 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 asin some Myoconche. ‘The muscular impressions are 
strongly marked, and often very rugose. The very young 
shells display neither striule nor punctures, and are scarcely 
to be distinguished from the smooth variety of the next species. 
Tong. 2 5, tati1°38, alé..1°3. 
Hah.—Mazatlan; abundant, but always rubbed; L’pool & 
fTavre. 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 MULTIFORMIS, 2. s. 
M. t. parva, maxime variante, sed plerumque angustd, 
prope cardinem tuimidd, angulo perobscuro diagonali ; margine 
