OF CONCnOLOGY. 41 



OBSERVATIONS ON THE GENUS lO. 



BY GEORGE W. TRYON, JR. 



The first species of this singular and beautiful genus was 

 described by Mr. Say, nearly fourty years ago, as a Fusiis. — 

 He remarks, " From the name of the genus it might reasona- 

 bly be supposed to be a marine shell, but it has never been 

 discovered on the coast, and seems to be limited to a very 

 small district of Holston River, in company with Unio cariosus, 

 suhtentus, Nobis ; Melanla svhglohosa, Nobis, and no doubt 

 other fluviatile shells. When the inhabitant becomes known 

 it may authorize the formation of a new genus, but there ap- 

 pears no character in the conformation of the shell that would 

 readily distinguish it fromi^;/s?/s." 



Mr. Lea, in describing lo spinosa, remarks, ' Prof. Troost 

 informs me that they are rare in the river, that they had been 

 observed in the graves of the aborigines, and it was generally 

 believed that these were ' conch shells' consequently coming 

 from the sea, it was urged that the inhabitants who possessed 

 them must have come over the sea. It does not appear that 

 they had been observed in their native element, though living 

 at the very doors of the person who had remarked them in the 

 tumuli.' 



Mr. Lea proposed the generic name lo for these shells in 

 1831, and Swainson in 1840 called them Melafusus. Until the 

 year 1860 only three species were known ; in February of that 

 year Mr. Anthony described, in the Proceedings of the Aca- 

 demy of Natural Sciences, four additional species. 



Mr. Reeve published, in April of the same year, a magnifi- 

 cent monograph of the genus in his Conchologica Iconica, 

 adding four more species by Mr. Anthony, and one of his own. 



Mr. Lea has recently described eight species which he pro- 

 poses to consider a distinct group of lo, but I cannot distin- 

 guish them from Pleurocera. The longer fuse, sharp lip and 

 fragile texture of most of these species, shows them to be im- 

 mature shells, and in several instances I had do difficulty in 

 proving them identical with mature shells described by Mr. 

 Lea as Trypanostoma {^Pleurocera,) by means of series of speci- 

 mens of different ages. 



Excluding these, twelve species have been described ; of 

 which we propose to retain five, regarding the others as sy- 

 nonyms. 



Many naturalists consider the genus to be restricted to one 



