290 REPORT ON ALBATROSS MOLLUSCA DALL. 



Only detached valves of this handsome and strongly sculptured 

 species were obtained. Its nearest relative is a Korean species repre- 

 sented by an imperfect valve collected by Captain St. John, in the Jef- 

 freys collection. The Korean shell is less strongly furrowed and the 

 furrows are more longitudinal than in the present species. P. cymata 

 is notable also for the crenulation, or rather the vertical grooving of 

 the internal basal margin, a feature I do not remember noting in any of 

 the other species. The pallia 1 line is more irregular as it nears the pos- 

 terior adductor scar than in the type of the genus, but it does not show 

 a definite sinus as in Dermatomya. The species is evidently very near 

 the border line and its septum will probably be found to be less muscu- 

 lar than in such species as P. granulata. 



Subgenus CETOMYA Ball. 



Poromya microdonta sp. nov. 



Plate vin, Fig. 6. 



Poromya sublevis Dall, Bull. Mus. Comp. Zool., xvill, p. 448, 1889; not of Verrill. 



Hab. — U. S. Fish Commission Station 2723, in 1,G85 fathor.s, ooze, 

 about 125 miles eastward from Chesapeake Bay, bottom temperature 

 not taken, but that of the next station, near by, was 3G°.3 F. 



In this species, by carefully dissecting away the septum, which pre- 

 sented much the same appearance as that of P. granulata in Pelseneer's 

 diagram (op. tit., PI. in. Fig. 7), several interesting facts were disclosed. 

 The posterior lamellae were not separated by fissures at their base. This 

 seemed evident on an external view, but was made more certain by an 

 inspection of the upper surface of the septum, where these openings, 

 wheu they exist, are always conspicuous. The anterior areas were fis- 

 sured, especially near the foot, but less so behind, so that when I first 

 examined this species, taking the extreme delicacy of the membranes 

 into account, and the .apparently imperforate character of the posterior 

 areas, I suspected that the fissures were due to tearing or incautious 

 probing. A reversal of the septum and an examination of other species 

 showed, however, that there are variations in this respect, and that 

 IViseneer had correctly described the conditions which exist in some of 

 them. An interesting feature disclosed by the examination of the sep- 

 tum under transmitted light was, that the blood-vessels which supply 

 the branchial lamella? appear to reach them from behind, a separate 

 vessel starting from the vicinity of the siphons and running a some- 

 what irregular course to each of the lamellar areas on each side. There 

 seemed to be no continuation of these vessels anteriorly in front of the 

 areas which they serve. The ovisacs are not lobulated, as in Myonera, 

 but more evenly spread over the posterior surface of the visceral mass. 

 The ripest eggs were large and conspicuous. There was no evidence 

 of their extrusion through the covering of the visceral mass, as in 

 Myonera, though this may take place later. 



