216 
The only si3ecimen of this species sent me was found in too bad a state 
of preservation to allow of me taking the the exact dimensions, or to give all 
the characteristics. I must, therefore, content myself with giving the figure 
and description published by Mr. E. McCoy. 
Relations and Differences . — This species is easily distinguished from 
the j)receding, the only one it appears to resemble, by its more elongated and 
more dej)ressed form, and also by the more decided truncation of its posterior 
margin, and the sinuosity of its ventral margin. 
Horizon and Localities. — Professor McCoy says it is common in the 
fine-grained sandstone of Wollongong. The only specimen I have received 
is very badly preserved, and was found in a greyish sandstone at Mt. Vincent. 
Pachtdomus ovalis, R. McCoy. 
PI. XIX, Eig. 3.' 
Rachydomus ovalis, E. McCoy, 1847, Ann. Mag. Nat. Hist., XX, p. 302, pi. 14, fig. 4. 
This is a rather oblong and oval shell, with moderately deep valves, 
and rather thick anterior beaks. The posterior edge is slightly angular ; the 
anterior rounded, forming a curve of short radius to unite it with the hinge 
line ; the ventral edge is rather regularly arched. The surface is ornamented 
with strong concentric, unequal wrinkles of growth ; the lunule is oval and 
deep ; and the external ligament rather well developed. The interior of the 
valves is almost perfectly smooth. The anterior and posterior impressions of 
the adductor muscles are large and oval ; that of the retractor of tlie foot is 
narrow and semilunar, surrounding the posterior half of the impression of the 
anterior adductor muscle. According to Mr. McCoy the pallial imjDression is 
slightly sinuous towards tliat part which touches the posterior muscular 
impression ; but I could not determine this. 
Dimensions . — ^The length is fifty-five, the breadth forty-five, and the 
thickness about twenty millimetres. 
Relations and Differences. — This differs from P. ylohosus by its 
surface ornamentations, and by its lesser thickness ; it difibrs from P. cyprina, 
and P. intrepidus, J. D. Dana, by its much greater relative iDreadth, and by 
the form of its external concentric folds. 
Horizon and Localities. — According to McCoy it is very abundant 
in the Wollongong sandstone. 
