AND DESCRIPTIONS OF NEAV SPECIES. 119 



passing obliquely from the beaks to the margin ; cardinal teeth large, 

 double in both valves, very erect and deeply cleft in both valves ; lateral 

 teeth short and lamelliform ; anterior cicatrices distinct ; posterior cica- 

 trices confluent ; dorsal cicatrices situated within the cavity of the shell 

 on the under part of the cardinal tooth and on the plate between the 

 cardinal and lateral teeth ; cavity of the beaks very large and rounded ; 

 nacre white and very pearly. 



Remarks. — This species is very closely allied to the U. ovatus (Say) 

 and U. occidens (Nobis). It differs constantly, however, from both, in 

 being more produced posteriorly, and in the position of the beaks 

 which are placed nearer the anterior margin. It is less flattened on 

 the posterior slope than the ovatus, and less carinate than the oceidens. 

 Like both these species the anterior section of the cardinal teeth is the 

 most elevated. In some specimens no rays ai-e observable*. 



Unio Pileus. Plate XVIII. fig. 47. 



Testa siibtriangulari, ventricosd, prcBclivo umboniali in longum subsulcatd, 

 emarginatd; valvulis crassis; radiis capillaribus; dentibus cardinalibus magnis, 

 lateralibus breviusculis subcurvisque; margaritd alba et iridescente. 



Shell subtriangular, ventricose, slightly emarginate, longitudinally furrowed in 



* Since this supplement went to press I have seen in the fine collection of that excellent 

 conchologist, Mr \V. Hyde, a specimen sent him by Mr Barnes some years since as U. ven- 

 tricosus. If this specimen be not of the same species as the above described, it certainly very 

 closely resembles it. Never having seen the individual specimen described by Mr Barnes as 

 v,entricosus, I believed, from that part of the description in which he says " this shell is more 

 capacious than any other of the genus hitherto described," tiiat he meant the species known to 

 us as globosus, and therefore I selected of the two species that which seemed to agree the least 

 with his description, and figured and described it. Should it, upon further examination, prove 

 that I have described the same shell with Mr Barnes, the name oC globosus should be used to 

 distinguish this capacious species, specimens of which are in the cabinets of Mr Hyde, the 

 Academy of Natural Sciences, Peale's Museum, and in my own. Mr Barnes must, I think, be 

 in error in supposing the ventricosus to inhabit the Delaware, or New Jersey near New York. 

 I do not think that any of the group belong to our eastern waters. 



