AND OTHER FAMILIES. 149 



Remarks. — Among the Uniones there is a group to which this species 

 naturally belongs. This group is characterized by the imperfection of 

 the hinge, the cardinal teeth being so immature as to present scarcely any 

 thing but lobes. Like the soleniformis it lives under stones and other 

 protected places. In the present species the tooth of the right valve 

 shuts before that of the left, and the lateral teeth, if not entirely want- 

 ing, are obsolete. The group, as far as I know it at present, consists 

 of the U. oriens (nobis), U. soleniformis (nobis), and the present species. 

 In size and outline of the margin, this species resembles the U. iris 

 (nobis). It has not, however, the brilliant nacre, nor the fine rays of 

 that species, and in the conformation of the teeth it differs very much. 

 Some individuals vary from the cylindrical form, being somewhat com- 

 pressed. As a mark of respect for the talents of Dr Hildreth, and his 

 assiduity in promoting a knowledge of the natural history of his vici- 

 nity, I dedicate this species to him. 



Unio Schoolcraftensis. Plate III. fig. 9. 



Testd subrotundatd, subxquilaterali, compressd, post clivum umboniale subtu- 

 berculatd ; valvulis subcrassis ; nutibus prominentibus ; epidermide fulvd, lato- 

 radiatu ; dentibus cardmalibus prominentibus, lateralibus laminatis rectisque ; 

 margaritd alba et iridescente. 



Shell subrotund, nearly equilateral, compressed, slightly tuberculated behind the 

 umbonial slope ; valves rather thick ; beaks elevated ; epidermis yellow with broad 

 rays ; cardinal leelh elevated ; lateral teeth straight and lamellar; nacre pearly white 

 and iridescent. 



Hab. Fox River of Green Bay. Mr Schoolcraft. 

 Cabinet of the Academy of Natural Sciences of Philadelphia. 

 Diam. -7, Length 1-1, Breadth 1-3 inches. 



Shell subrotund, somewhat angular at posterior dorsal margin, nearly 

 equilateral, compressed, slightly tuberculated posterior to umbonial 

 slope ; substance of the shell rather thick ; beaks elevated ; ligament 

 short ; epidermis smooth, somewhat yellow, with several broad green 

 rays — that over the centre of the disk being broadest ; cardinal teeth 

 40 



