Til 1C NAUTILUS. 75 



253 (proposed as a snbgenus of (_'yt//erea ; type and sole species 

 Cytherea crassatelloides Conr.). 



Trigonella Conrad, 1849. Journ. A. N. S., Phila., I, 213 (diag- 

 nosis of genus). 



Pachydesma Conrad, 1854. Proc. Acad. N. S., Pliila., vii, p. 31 

 (" note on the genus Trigonella Con. This name being superseded, 

 I propose to substitute that of PacJtydesma"). 



Prior to 1843 no description of Donax stullorum was published 

 not a line except the name and the locality, " Indian Seas." The 

 specimen figured by Mawe is young, and apparently the color- var. 

 tr iserialis. 



The first description was by Hanley in 1843. Gray merely refers 

 to the plate in Index Testae. Suppl., not even to Mawe's earlier 

 publication. 



Query : Should Mawe's figure, which is quite recognizable, but 

 without description and with a false locality and erroneous generic 

 reference, displace Conrad's name, which was from a known locality, 

 was well defined, and was accompanied by a good figure of the typi- 

 cal many-rayed shell ? 



NEW SOUTHERN UNIOS. 



BY BERLIN H. WRIGHT. 



Unio singularia, s 



Shell uniformly and moderately solid, wide, rather inflated and 

 very inequilateral. Surface silicate, with distant growth lines; 

 epidermis dark olive, ray less, finely wrinkled, and towards the base 

 becoming fuscous; dorsal margin slightly arched, anterior margin 

 abruptly rounded, base straight or subemarginate, posterior margin 

 bluntly rounded or biangulated ; beaks not prominent, and sur- 

 rounded by five or six sharp concentric ridges which gradually 

 merge into the sulcations on the umbos ; umbonal ridge bluntly 

 rounded ; lateral teeth erect, solid, straight, widely separated from 

 the cardinals and, in the left valve, from each other, single in the 

 right and double (?) in the left valve, the superior division possessing 

 scarcely prominence enough to warrant calling it a tooth ; cardinal 

 teeth solid, double in the left and single in the right valves ; the single 

 one being deeply serrated on its summit ; beak cavities very slight; 



