858 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



YOLDIA Moller, 1842. 



Toldia VERRILI, and BUSH, Amer. Journ. Sri., Ill, pp. 55, 62, figs. 12, 16, ,T;mn- 

 :iry, 1897. 



Type. YohUa hyperborea Torrell= Toldia arctica Moller (not Gray). 



We have restricted this genus to the typical forms, such as T. lima- 

 tula (Say), I" sapotiUa (Gould), Y. myalis (Couthouy), and many closely 

 allied foreign species. 



These have a nearly smooth, compressed, lanceolate, gaping shell, 

 more or less prolonged and tapered posteriorly, with a poorly denned, 

 wide rostrum, generally without carinatious. The external ligament is 

 marginal, feebly developed, continuous under the beaks, and not much 

 differentiated from the general epidermis. The ehondrophore is large, 

 concave, and projects within the margin. The pallial sinus is large 

 and deep. The siphon tubes and posterior pallial tentacle are long. 

 The palpal tentacles are long and tapered; in life they may extend 

 nearly to the end of the expanded siphon. 



ADRANELLA, new subgenus of Yoldia. 



Type. Adranella casta, new species. 



This subgenus is allied to Yoldia, but is distinguished by its oblong- 

 ovate, compressed form, with a broadly rounded, posterior end, having 

 a very small, nearly obsolete, rostrum. Surface sculptured with dis- 

 tinct, raised, concentric lines. Hinge plate and teeth strong. Resilium 

 occupying a distinct pit in the apex of a large shelf-like, triangular 

 chondrophore. 



YOLDIA (ADRANELLA) CASTA, new species. 

 (Plate LXXX, fig. 4.) 



Shell small, oblong-ovate, somewhat compressed, inequilateral, with 

 the posterior end a little the longer and considerably the broader. 

 Urnbos small; beaks curved inward and slightly backward. Antero- 

 dorsal margin slightly concave near the beak, a little convex opposite 

 the distal teeth; anterior end a little narrowed, obtusely rounded; 

 ventral margin broadly and evenly rounded with a very faint undu- 

 lation posteriorly; postero-dorsal margin a little convex, sloping less 

 than the anterior, and turning up at the end so as to form a slight, 

 hardly distinct rostrum. The hinge-plate is rather large and thick, 

 especially distally on each side, becoming narrow and turning upward 

 at the beak, where it is interrupted by a small, rather deep resilial 

 pit, which is bordered interiorly by a thickened extension of the hinge- 

 margin forming a sort of shelf, the whole constituting a broadly trian- 

 gular chondrophore with the pit near its apex. The anterior series of 

 teeth contains twelve, of which three or four proximal ones are very 

 small, and form a series which curves upward, exterior to the chondro- 

 phore, and terminates at the superior margin of the shell; the teeth 





