dall: mollusca and brachiopoda. 423 



anterior, and 3-75 mm. from the posterior end; surface irregularly concentri- 

 cally ridged, a line from the beaks to the lower posterior angle sets off a subtri- 

 aiigular space on which the periostracum is slightly rougher and darker than on 

 the rest of the shell ; posterior end slightly gaping ; interior white, polished ; left 

 valve with a prominent chondrophore, the anterior ridge upon which is unusually 

 strong ; the chondrophore is arcuate somewhat obliquely downward ; the pallial 

 sinus is large, rounded, and reaches forward in a vertical sense about to the pos- 

 terior end of the chondrophoric ridge alluded to. Lon. of shell, 7 ; alt. 4 ; 

 diam. of left valve, 1 mm. 



U. S. S. "Albatross," station 2779, in Magellan Straits, in about 20 fathoms, 

 gravel, one left valve. U. S. N. Mas. 110,719. 



No species of the genus has hitherto been reported from the Magellanic region, 

 and so this solitary valve has a certain interest. It is more nearly equilateral 

 than any of the other species. 



Corhulidae. 

 CORBULiA (BRUGuiiiRE) Lamarck. 

 CUNEOCORBULA Cossmann. 

 Corbula (Cuneocorbula) ira Dall, n. ep. 



Shell of moderate size, solid, short and high, whitish covered by a chestnut 

 brown periostracum ; valves inequilateral, the posterior end longer, nearly equi- 

 valve, the right valve smaller; disk uniformly sculptured with narrow concentric 

 channels, separated by wider, rounded but not cordhke ridges, about two to a 

 millimeter ; beaks high, prominent ; anterior slope 4.5°, short, the anterior end 

 attenuated and rounded ; base arcuate ; posterior end acute, its dorsal slope 

 formed by a wide truncation, bounded by a sharp angle outwardly ; within, close 

 to the dorsal margin, is a feeble rounded ridge on each valve, ending distally in an 

 obtuse angle ; between the outer and inner ridges the area is slightly concave 

 and concentrically threaded ; in front of the beaks there is a small depressed 

 space but no circumscribed lunule ; basal margin, with regard to a vertical longi- 

 tudinal plane, slightly flexuous ; left valve edentulous with a small triangular 

 cartilage pit ; right valve with a small recurved tooth in front of the pit ; interior 

 smooth, yellowish white ; pallial line truncate behind but with no sinus ; margins 

 entire. Lon. of shell, 11.5 ; of anterior end, 3.2 ; alt. 7.5 ; diam. 6.0 mm. 



U. S. S. "Albatross," station 3355, Gulf of Panama, in 182 fathoms, mud, 

 bottom temperature 5 l°.l F. U. S. N. Mas. 122,944. 



This species is unlike any of those from shallow water in the Panama region, 

 and somewhat resembles C. frnoxiana Adams, from Jamaica, which is more elon- 

 gate and has three instead of two ridges on its posterior area. 



