MAZATLAN BIVALVES 167 



It is so easy in thin Anomiadse to see the muscular scars one 

 expects, that I had sketched 3 scars for this species to shew 

 the difference in arrangement from those of A. lampe, of which 

 many conchologists had considered my valve a variety. Having 

 however found a pair, and being struck by the V-shaped notch 

 at the cardinal end of the hole, I re-examined the scars, and 

 found the supposed third to be only one of those non-muscular 

 impressions which are very liable to deceive beginners till they 

 have learnt from books what they ought to look for. Shell 

 extremely like Anomia lampe (smooth var.) ; from which it is 

 known at once by the brown disk, inside which is a very faint 

 white disk, with the extremity rounded, not triangular. It is 

 known from P. foliata by the entire absence of radiating 

 striae, which are very conspicuous in young shells of that 

 species. A remarkable feature in this shell is the sharp white 

 lamina, (or clavicle,) which runs from the hinge in the lower 

 valve, near the hole but not parallel with it, losing itself in a 

 thin white deposit in which is the muscular scar. This clavicle, 

 or lengthened support to the cartilage plate, is also seen in P. 

 Cumingii, large, rounded, and running in a straight line to the 

 muscular scar. It is more or less developed in some other 

 species of the genus ; but is remarkable in this for its length, 

 direction and sharpness. Long. 1*12, lat. 1'46, alt. '16. 

 Hob. Mazatlan ; one pair and a valve with Anomise; L'pool 



Col. 



Tablet 750 contains the pair. 



GENUS ANOMIA, Linn. 



\- 219. ANOMIA LAMPE, Gray. 



Proc. Zool. Soc. 1849, p. 117 ; B. M. Cat. Anom. p. 19, sp. 



14. C. . Ad. Pan. Shells, p. 244, no. 377. 



This shell in its ordinary state would hardly be known by 

 the meagre description in the B. M. Cat. ; but the very numer- 

 ous finely grown specimens sent in this collection give oppor- 

 tunity to record its leading features. Many hundreds were 

 sent carefully packed ; but most have been broken since they 

 came to this country. There was also a box of valves, many 

 of them extremely brilliant, from which I picked the valve of 

 P. claviculata ; doubtless there were many other treasures in 

 it, but it was unfortunately sold off to make ladies' fancy work 

 before I had an opportunity of examining it. 



