TO 188ft"'] PEOCEEDINGS OF THE NATIONAL MUSEUM. 281 



simple oblique upper cuds of the septal orifices. What can their office 

 be ? I suppose that they serve to admit fresh water to the upper cham- 

 ber, which I believe to be utilized in some, if not all, instances as a 

 marsupium. It is probable that by, suitable muscular contractions, 

 the septum will operate somewhat like the washer of a pump valve, and 

 that the upper chamber can be filled or emptied of its contained water 

 at will. 



I believe the septum m~ Cuspidaria to be homologous with the ordi- 

 nary siphoual septum, only more prolonged ; and that its muscular tis- 

 sue is the equivalent of the siphoual retractors of ordinary Pelecypods. 

 I do not regard it as in any manner homologous with the normal cteni- 

 dia. 



Cuspidaria (?) monosteira sp. nov. 



Plate vni, Fig. 5. 



Shell small, inflated, stout and strong, with a single strong vertical 

 keel and much fainter concentric sculpture ; color white, with a very 

 thiu, pale epidermis ; umbones nearly central, anterior end evenly 

 rounded from the beak to the basal end of the keel; posterior end 

 rostrate, the rostrum short, wide, abruptly truncate; concentric sculp- 

 ture of rather strong incremental lines, which at first are varied by 

 regularly spaced, rather sharp, distant, elevated lines; later these become 

 obscured in the stronger, more crowded, and rather irregular incre- 

 mental lines ; a faint ridge extends from the beak to the lower angle of 

 the rostrum, the only other radial sculpture is the exaggerated, high, flat- 

 topped, vertical keel; this projects from the rounded base and inter- 

 rupts its curve; interior smooth, scars hardly perceptible; in the left 

 valve the hinge-line is arched or rather angulated in the middle ; there 

 is a strong posterior lateral tooth, no anterior lateral or any cardinal 

 teeth; the fossette is small, posteriorly inclined, and continuous with 

 the margin of the hinge ; maximum longitude of shell 5 ; altitude 4.25; 

 diameter 5 mm . 



Hab. — U. S. Fish Commission Station 27G0, 90 miles north from 

 Ceara, Brazil, in south latitude 12° 7', west longitude 37° 17', in 10 19 

 fathoms, bottom temperature 39°.4' F. 



Only a left valve of this remarkable and very characterististic little 

 shell was obtained. As the left valve is the uncharacteristic one as 

 regards the hinge, it is not practicable to say to which section of the 

 genus this species should be assigned, but its characters agree with 

 those of the left valve of Necera pulchella H. Adams. 



Cuspidaria (Cardiornya) striata Jeffreys. 



This species which ranges northward to the Arctic Seas and whose 

 southernmost known range was Florida Strait, was collected cast from 

 Rio Janeiro, at Station 27G2,'in 59 fathoms, muddy bottom. This gives 

 an immense extension of its southward range. 



