Welter — Kinderhook Faunal Studies. 29 



beak; posterior impression about equal to the anterior one 

 in size, situated near the posterior margin at about one half 

 the height of the shell ; the two muscular impressions con- 

 nected by a regularly curved, continuous pallial line. 



Remarks. There seems to be no apparent reason for sep- 

 arating this little shell from Northview, from Ptychodesma 

 minor which was originally described from the Chemung 

 Group near Elmira, New York. Hall's* illustration of the 

 species agrees almost exactly with the best specimen observed 

 from Northview. Only the general form and proportions of 

 the shells can be compared, however, and as these are usually 

 not entirely safe criteria for the comparison of pelecypods, 

 it is thought best to make the identification provisional. It is 

 questionable whether the species should be referred to the 

 genus Ptychodesma. The generic characters are not shown 

 in the Northview specimens, nor, judging from Hall's descrip- 

 tion and illustration, are they clearly shown in the New York 

 specimens of P. minor. 



Macrodon sp. 



PI. Ill.f. 8. 



The larger specimens about 30 mm. in length, the height 

 about half the length ; the hinge-line and basal margin sub- 

 parallel. Basal margin straight or gently curving, sometimes 

 slightly sinuous at about the middle ; anterior margin broadly 

 rounded below but nearly straight above, meeting the hinge- 

 line at an acute angle; posterior margin rounded below, 

 obliquely truncated above. Hinge-line straight, about equal 

 to the greatest length of the shell. Valves gibbous in the 

 umbonal region, with a prominent, rounded, undefined 

 umbonal ridge extending to the posterior basal extremity, and 

 with an undefined flattened or slightly depressed area extend- 

 ing from the beak to near the center of the basal margin. 

 The posterior cardinal slope concave. Beaks prominent, 

 elevated above the hinge-line, situated at about the anterior 

 fourth of the total length of the shell. Surface marked by 

 irregular concentric lines of growth and by fine radiating 

 striae. 



* Pal. N. Y. 51 : pi. XLI. f. 27. 



