NO. 1139. DEEP-WATER MOLLVSCAVERRILL AND BUSH. 873 



rior acute, curved, V-shaped teeth; at the proximal end of the posterior 

 series, in the left valve, there is an oblong, prominent, tooth-like process, 

 much larger than the adjacent teeth. Three or four of the distal teeth, 

 on each side, are decidedly large, prominent and acute with the tip 

 curved outward, but the si/e decreases regularly toward the center. 

 There is a well developed dark ligament, visible externally, both before 

 and behind the beaks. The surface is covered by relatively rather 

 large, distant, concentric ridges and furrows, easily visible under a lens, 

 which are everywhere covered by very regular microscopic lines and 

 grooves of about equal width. 



Length of the largest valve, 4.25 mm.; height, 2.8 mm. 



A few specimens, at four stations, between N. lat. 39 49', W. long. 08 

 28' 30", and N. lat. 30 47', W. long. 73 9' 30", in 1,451 to 1,685 fathoms, 

 1883-1886. 



This species is remarkable for its oblong-ovate form and very regular 

 concentric sculpture, consisting of fine ridges and furrows which are in 

 turn everywhere covered with regular microscopic lines. This species 

 was at first thought to be I", expansa (Jeffreys) which it resembles in 

 form, but additional specimens and more careful study show that the 

 species are very distinct. In I", expansa the hinge-margin is much 

 straighter, the teeth fewer and different in form, the resilial pit very 

 different, the two ends of the shell more nearly equal, and the sculp- 

 ture quite different. 



Our species differs considerably from the typical forms of Yoldiella 

 in having a more oblong form with both ends evenly rounded, a well- 

 developed ligament, and a more evident resilial fossette or choudro- 

 phore which, however, is situated decidedly below the hinge-plate. 

 The existence of a peculiar tooth-like process adjacent to the resilial 

 notch would be a character of considerable importance were it con- 

 stant, but the specimens show great variation in its development; in 

 some, it is even almost abortive. These distinctive characters, although 

 important, seem hardly worthy of generic distinction. 



Subfamily 



MALLETIA Desmoulins, 1832 (restricted). 

 Mallet ia VERRILL and BUSH, Amer. Journ. Sci., Ill, pp. 56, 63, January, 1897. 



Type. MaUetia clnlensis Desmoulius. 



We have restricted this group to those species having a nearly 

 smooth, somewhat compressed, oblong or elliptical shell, blunt pos- 

 teriorly, without any definite rostrum or carination. The carinated 

 and rostrated species that have been placed in it will thus be referred 

 to Neilo H. and A. Adams. The resiliuin is wanting, or else represented 

 by a special part of the ligament, external to the teeth. The ligament 

 is well developed and prominent. The siphon tubes are long and 

 united nearly to the tips. 



