369 



ened in front; upper valve thinner, white, somewhat radiately 

 rugose, internally with two elevated ridges diverging from the centre 

 towards the posterior lateral margin ; umbo somewhat posterior. 

 From the Mediterranean. In Mr. Cuming's collection. 



HIPPONYX. 



Testa insequivalvis, subaequilatera, valva inferiore affixa, com- 

 pressa, margiue plerumque elevato; valva superiore subconica, 

 vertice ad marginem posticum inclinato ; impressionibus muscu- 

 laribus in utraque valva duabus, postice coalescentibus, formam 

 ferri equini conjunctis exhibentibus ; cardine et ligamento cardinis 

 nullis. 



Shell inequivalve, nearly equilateral, attached by the lower 

 valve, which is compressed and its margin generally thickened ; 

 upper valve somewhat conical, rather inclined toward the posterior 

 margin, muscular impressions two in each valve, when taken 

 together somewhat in shape like a horse-shoe, those of the upper 

 confluent posteriorly. 



Distinguished and proved to be a bivalve by Defrance, who first 

 met with the two valves together in a fossd species. The species 

 have usually been called Patella, because the upper valve alone 

 was known. Very rarely the two valves have been met with 

 together. Several species in this complete state have been dis- 

 covered and brought to this country by Mr. Cuming, from whose 

 Collection our drawings have been taken. 



1. Hipponyx barbata (pi. lxxiii. f. 26, 27.) Sow. Zool. Proc. 

 1835. p. 5. 



Testa, palhde fulva, subelevato-conica, radiatim confertim striata ; 

 margine ventrali producto ; epidermide pilosa, margine interno 

 crenulato. 



Shell pale yellowish brown, of a slightly elevated conical form, 

 covered with radiated close-set striae ; ventral margin produced ; 

 inner edge crenulated ; epidermis coarsely hairy. 



Pound on the Coral reefs around Toobouai, one of the Society 

 Islands, by Mr. Cuming. 



2. Hipponyx Mitkula (pi. lxxiii. f. 18, 19, 20.) Befr. I. c. 

 Pileopsis mitrula, Lam. Patella mitrula, Auctm. 



Testa alba, depresso-conica, concentrice lamellosa, lamellis sub- 

 confertis, radiatim striatis ; epidermide pilosa. 



