222 ANNALS NEW YORE ACADEMY OF SCIENCES 



latter) than the lateral plications. The sinus is flattened or perhaps very 

 obscurely elevated along the median line, but no median plication is developed 

 in it, and no corresponding sulcus has been observed along the fold. The 

 lateral plications number from 5 to 7 on either side of the sinus. The sculp- 

 ture consists of regular, transverse, imbricating lamellre. 



Hustedia multicostata sp. nov^ 



Shell rather large, a length of 13 mm. being about the maximum observed. 

 Shape regularly ovate, broad in some specimens, narrow in others. Convexity 

 moderate to high, about equal in both valves. 



The ventral valve has a distinct though undefined sinus and a beak moder- 

 ately projecting and incurved. 



The dorsal valve is without a distinct fold. Its cardinal line is short. 



The surface is marked by from 25 to .32 gradually enlarging costse. When 

 unexfoliated, these are high and narrow and separated by striae of about their 

 own width. When exfoliated, the ribs are narrow and abruptly elevated from 

 broad, flat interspaces. 



Composita subquadrata var. lateralis var. nov. 



The shells included under this title are rather large with a subquadrate 

 shape and strongly elevated fold and sinus. The sides are extended and 

 sharply rounded. 



In the ventral valve, the sinus begins as a narrow depression and re- 

 mains so until the shell is about half grown. Then it becomes the 

 median line of the real sinus, which then develops with rapid increase of 

 width and depth. The fold is developed with equal rapidity, when it 

 once begins to appear, being defined by two strongly diverging grooves, 

 which curve downward, and, if it were not for the fact that they appear 

 to bend backward at their posterior end, are so directed that they would 

 intersect some little distance in front of the posterior margin. 



Composita acinus sp. nov. 



Under this title is subsumed a group of diminutive shells which have, 

 in spite of their size, characters indicating maturity. They are elongate, 

 ovate and highly convex. The ventral valve has a fairly prominent in- 

 curved beak and a moderately deep, narrow sinus. The dorsal valve does 

 not develop a distinct fold to correspond to the sinus of the ventral, the 

 effect of wliich is often to produce an emargination of the anterior out- 

 line, an effect which is in some instances enhanced by the circumstance 

 that the dorsal valve not only does not develop a fold but sometimes 

 develops a median sulcus of its own. 



