NO. 1185. SYNOPSIS OF THE SOLENIDJE— BALL. Ill 



In this connection I may add some supplementary data to my 

 "Synopsis of the Psammobiidne,"^ which have come to hand since that 

 article was printed. 



Tagelus gihhns Spengler, as typically restricted, passes as far south 

 as St. Thomas, West Indies, and i)robably to the northeast shores of 

 Brazil. The variety called T. platensis by d'Orbiguy diHers by being- 

 shorter aud more attenuated behind, and I have seen it only from the 

 southern coast of Brazil and Uruguay. In all the typical species of 

 Tagelus the posterior end is shorter than the anterior, the pallial sinus 

 is deep, reaching to or forward of the perpendicular from the umbones, 

 and the posterior adductor scar is rounded. The teeth are simple, 

 erect, pedunculated, t\YO in each valve. There is no central constric- 

 tion or internal rib. Curiously enough, the shell figured by H. and A. 

 Adams to illustrate Tagelus (or Siliquaria) gihhus is a N'ovaculina, 

 while they describe the teeth as 3:2 (which is the dentition of JSFovacu- 

 lina) and the siuns as deep beyond the umbones, which belongs to 

 Tagelus and is untrue of Novaculina. 



Owing to the fact that a number of externally similar but really dif- 

 ferent shells have been confused, the diagnoses of these groups are 

 frequently inaccurate, and I have therefore reviewed the question in 

 the light aflbrded by the specimens. The following are the characters : 



Genus NOVACULINA Benson, 1830. 



Type. — N. gangetica Benson. 



Beaks subanterior; teeth (when fully developed) three in the left and 

 two in the right valve; the anterior left tooth often obsolete or wanting, 

 the anterior right tooth bifid; there is no median constriction, the pal- 

 lial sinus is small, not reaching the beaks, the posterior adductor scar 

 rounded ; the scar of the ventral side of the sinus not coalescent with 

 the pallial line below it; situs in fresh water. 



Section ClUNACtTlUM Ball. 



Tyije. — Solecurtns mollis (Gould) Sowerby, Conch. Icon. Solecurtus, 

 1874, pi. VI, fig. 26; coast of Brazil and Uruguay. 



Valves obliquely constricted, the constriction reflected by an internal 

 thickened elevation (not a clavicle); beaks subanterior; teeth, two in 

 the left and two in the right valve, the posterior left tooth bifid, in 

 some of the species there is an obsolete tooth behind it; the pallial 

 sinus not reaching the beaks, the posterior adductor scar triangular, 

 the scar of the sinus coalescent ventrally with the pallial line; situs 

 marine. 



Genus TAGELUS Gray, 1847. 



Type. — Solen gibbus Spengler. 



Valves not constricted and without a clavicle; beaks medium or sub- 

 posterior; teeth simple, pedunculate, two in each valve; pallial sinus 



' Proc. Acad. Nat. Sci. Phila., 1898, pp. 57-62o 



