78 BULLETIN OF THE LABORATORIES 



truncate above ; finally, we are not sure the hinge structure is that of 

 Edmondia. 



To all appearance our specimens agree with the smaller form fig- 

 ured in Vol. V, Pal. N. Y. ,.Part I, under the name Macrodon ovatus, 

 though its relation to the typical larger form is less obvious. In some 

 of our specimens the teeth of Macrodon were doubtfully observed. 



Ctetiodonta {.Jfucida) iowensis, W. and W. 



(Plate I, Figs. 14, 17.) 



A nuculoid shell resembling the one quoted is very common in 

 the layer below congl. I. 



Shell small, triangularly subovate, quite ventricose. Beaks about 

 one-fourth or less from the anterior, prouMuent, acute, and incurved. 

 Hinge abruptly bent at a little less than a right angle with about 10 

 posterior and 4-5 anterior teeth, anterior margin obliquely truncate; 

 lower margin a nearly regular semi-elliptical curve. Surface marked 

 by numerous plicae, especially near the margin, where the epidermis 

 is thickened. Length 10.5 mm, height 8 mm, thickness 6 mm. (?) 



Ctejiodonta {Kuciila) stella, Win. 



(Plate IX, Fig. 14.) 



** Shell very small, elliptic-ovate, with sub-central beaks. Ante- 

 rior cardinal slope arched, posterior nearly straight ; extremities rather 

 .sharply rounded; ventral side semi-elliptic. Anterior hinge-plate with 

 17 minute, acute teeth; posterior with five. Beaks a litde attenuated 

 near the extremity, curved inwards and backwards. Shell thin, with 

 delicate concentric striae." 



This species occurs Avith C. iowensis, in shales below congl. I. 



Ctenodonta {J^ucula) houghtoni, Stevens? 



(Plate V, Fig. 17.) . 



A small species collected by Mr. Deming, in the shales over congl. 

 II. is very like N. ventricosa, H. 



Shell small, transversely sub-oval; height equal to -i the length; 



