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Genus — MYTILUS, Linnmis. 
Mytilus crassiventer, L. G. de Koninck} 
PL XXI, Fig. 2. 
This is an elongated, cuneiform, thick shell, very ventricose on the 
ventral side, where the tv/o valves approach each other abruptly, and fall 
nearlv vertically on their ventral margin, producing a nearly plain surface ; 
from the hinge line, on the contrary, they spread out at a gentle slope, and 
unite at a very acute angle. The posterior margin is rounded. The beaks 
are small and terminal. The impressions of the adductor muscles are oval, 
large, and very superficial, and placed at the posterior third of the shell. The 
surface must have been slightly and irregularly undulating. The shell 
appears to have been very thin. 
Dimensions . — The length is seven, the breadth three and a half, the 
thickness three centimetres. 
Delations and Differences. — In general form and in size this species 
resembles M. mosensis, Ryckholt; it differs by its much greater relative 
thickness, by its less curved hinge line, and by its surface ornamentation. 
Horizon and Localities. — A single cast of this species w^as found in a 
brownish sandstone at Branxton. 
Mytilus bigsryi, L. G. de Koninck.’^ 
PL XXI, Fig. 1. 
This shell is elongated, slightly arched, one-third longer than broad, 
and almost regularly ventricose. Its posterior side is rounded and very long, 
the ventral margin but little curved, and the beaks rather thick and terminal. 
The surface is covered with from twelve to fifteen strong, concentric, rather 
unequal undulations. The impressions of the adductors are very large, well 
marked, nearly circular, and placed towards the middle of the length of the 
valves. The shell, which seems to have been rather thick, is utterly unknown 
to me. 
Dimensions . — The length is six and a half centimetres, the breadth 
forty-seven millimetres, and the thickness thirty millimetres. 
* " \.Mytiloj)s (?). R. Etheridge, Junr., Geol. and Pal. Q’land., 1892, p. 272, t. 14, f. 20. — W.S.D. 
2 H 
