BALL: MOLLUSCA AND BRACHIOPODA. 377 



not defined ; anterior end evenly rounded, posterior more produced and attenuated 

 but not acute ; base evenly arcuate ; surface with concentric riblets closely adja- 

 cent, finer near the umboues, coarser and rounded near the base, extending over 

 the whole surface except the upper posterior part, where they become obsolete ; 

 interior polished, the scars hardly visible, the pallial sinus shallow ; hinge with 

 about eleven anterior and nine posterior, more or less folded teeth separated by a 

 deep though small resiliary pit. Lou. 4.5 ; Ion. of beaks behind the anterior end, 

 2.0; alt. 2.7; diam. 1.5 mm. 



U. S. S. " Albatross," station 3422, off Acapulco, Mexico, in 141 fathoms, 

 mud, bottom temperature 53o.5 F. U. S. N. Mus. 122,918. 



Easily distinguished from the preceding by its wrinkled surface and strongly 

 recurved rostrum, and from the Leda cordyla group by its olivaceous instead of 

 reddish brown periostracum. 



Leda (Leda) peruviana Dall, nom. prov. 



Shell large, slender, rostrate, with a dark brown periostracum, the surface 

 mostly smooth but with a few coarse irregular wrinkles on the basal half of the 

 disk anteriorly ; with about fifteen anterior and thirty-eight posterior hinge teeth ; 

 with a large obliquely posteriorly directed chondrophore, a short but strong longi- 

 tudinal septum in the channel of the rostrum, and no perceptible oallial sinus. 

 Lon. 22, anterior segment,/; alt. 9.5 ; double diam. 6.0 mm. 



A single decayed valve was dredged in 1036 fathoms, mud, off Aguja Point, 

 Peru, at station 4654. 



This resembles one of the pernula group of Arctic Ledas, but is clearly dis- 

 tinct from any other, reported from the region under consideration. 



Spinula Dall, subg. nov. 



Shell rostrate, acute behiud, smooth, with a well-developed short amphidetic 

 ligament, an internal resilium supported by triangular chondrophorcs, a defined 

 luuule and escutcheon ; a long, slender, completely united siphon, no palpal 

 tentacles; pallial sinus obsolete. Type, Leda calcar Dall. 



The type of this group has a hinge and ligament so strong that it has been 

 impossible to open a specimen without breaking the valves, and even then the 

 hinge would not separate. The resilium is black, plainly visible from below 

 within the shell. 



The animal has a long, contractile, slender siphonal tube, but there are no 

 pallial muscles for retracting it, and apparently no marked sinuation of the pallial 

 line. Mantle margin simple. Foot like that of Leda proper, the sole fringed 

 and rather short. Gills short, palpi strong but without any accessory tentacles. 

 The valves closed accurately. The adductor muscles seemed slender. The 

 ligameut is well devclojied and distinctly defined, short and about equally 

 extended on each side of the beaks. 



