406 



PALAEONTOLOGY OF NEW-YORK. 



slightly outwards, send off a short spur into the ventral cavity and are 

 thence directed forwards, and gently curving, join the median crest, to 

 which they are attached, forming a loop of peculiar character. The occlu- 

 sor muscular impressions have rarely been seen with any degree of dis- 

 tinctness; but the depressions just at the termination of the crural 

 processes, and on each side of the median ridge, are striated ; and this 

 striation often extends in a wide flabelliform expansion, probably due 

 to vascular impressions. Towards the margin, the interior of both valves 

 is strongly pustulose. 



The accompanying wood-cuts illustrate the parts referred to above. , 



FIO. 1. 

 Interior of the dorsal valve. 



•FlO. 2. 

 Longltadinal sectioo of the dorsal valve. 



j. Cardinal process. 



b. Crenulated teeth-sockets. 



c. Crural processes. 

 I. Loop. 



a. Septum. 



j. Cardinal process. 



b. Tooth-socket. 



c. Crural processes. 

 /. Loop. 



s. Septum. 



*Iu the punctate texture of this shell, it differs from either of the Genera Lep- 

 T^NA, Strophomena or Strophodonta ; but this might not he an objection to 

 admitting Tropidoleptus into the family, were the other characters coincident. 

 The area is longitudinally striated, and presents a different aspect from any of 

 the SiROPHOMExn)^-, but has analogy with some of the Orthidcs. The teeth are 

 not extensions of the lamellae bounding the foramen, but distinct from it and 

 deeply crenulate or lobed, and inserted into corresponding crenulate sockets in 

 the dorsal valve. The form of muscular impressions, so far as known, is not very 

 dissimilar to those of Strophomena or Ortiiis. 



In comparing the fonn of the cardinal process and its appendages, we shall 

 find it almost entirely similar to that of Leptoccelia, as shown in two authentic 

 species {L.flubellites and L.fiwhriala), and the muscular impression of the ven- 

 tral valve is quite like that of the same species. 



