288 NEW YORK STATE MUSEUM 



Crescence line diffuse, well curved, slope of surface of shell from 

 this line to either margin gently convex; greatest breadth of shell 

 on this jine about one third way from beak to posterior angle and 

 measures 7mm. The surface is lamellose and imbricated, lamellae 

 widen as posterior angle is approached and are there placed with 

 their edges something over imm apart; they project from the shell 

 about I mm or a little more and become crowded on the margin dur- 

 ing the gerontic stage. 



The valves seem to gape very slightly at the anterior extremity, 

 perhaps indicating a byssal opening. Area crushed in, but posterior 

 extremity of hinge line presents a well formed channel between the 

 winglike posterodorsal extension of the valves, as in U n i o 

 a 1 a t u s , as if to receive a parivincular, opisthodetic ligament. 

 The shell substance is rather thin near the middle of the valve and 

 becomes markedly thicker near the posterior margin. 



A line connecting a series of points placed at the successive posi- 

 tions of posterior extremity of shell (measured from the probable 

 position of the beaks) marks also the places of greatest breadth met 

 in crossing the shell and lies over the path of the successive positions 

 of, the posterior adductor. A line from apex to posterior extremity 

 of one of the earlier neanic stages, when the shell had attained about 

 one third its length, makes an angle of 30° with the hinge line; 

 during the growth of the remaining two thirds of the shell this line 

 is gradually turned away from the hinge line through an angle of 



an additional 27°. 



GASTROPODA . 



Genus ettnema Salter 



Eunema historicum sp. nov. 



Plate 4, figure 5 



Description. Shell small,^ turbinate, apical angle 80°, whorls 

 about four. The body whorl shows five well marked minutely tuber- 

 culate spiral costae with trace of a faint sixth at the broken edge, 

 well down on the base. The first costa (numbering down from 



^The type specimen, being broken diagonally across the lower portion of 

 the axis, has lost the aperture while the apex and most ot the body whorl 

 are preserved ; it has a hight of 4.3mm. 



