ol)() rAKBONIFEROUS FORMATIONS AND FAUNAS OF COLORADO. 



tlio speciineii iigurcd by Hull uiid C'iai'kc has these diuicu.sions unusuuiiy unequal; 

 11(11- are the sides, as a rule, straightened, as in the type specimen. Older examples 

 are proportionately more elongate than young ones. The ventral valve does not 

 project as far beyond the dorsal as in many species of Diiddnuia., and the beak is not 

 attenuate nor strongly incurved. The recurved pedicle sheath is often well 

 developed. 



The common shape of this species is more like that of C'ryptonella eudora. 

 Indeed, as the fossils from Licking County, Ohio, which have been identified with 

 the latter, come from almost the same horizon in the Waverl}' as the Sciotoville beds, 

 I feel some confidence that thej^ belong to this species. Should this prove to be the 

 case, it would be well to restrict the name eudora to the Devonian species and place 

 Cryjptondla eudora (pars) in the synonymy of C'ramena subellijJtica. 



Cr-anpena siibeUijriica resembles Or. ioioensis in the closest manner, and I am not 

 sure that, if similarly preserved, it would be easy to distinguish them. Oi. ioioensis 

 is apt to be more highly arched, with the beaks of both valves more attenuate and 

 produced. The surface is smoother and less interrupted by aj^preciable lines of 

 growth. The blunt, clums}^ form of the beaks in Cr. svhelUptica is rather noticeable 

 and chai'acteristic. 



In both Cr. suhelUptica and Cr. iowensis the hinge plate is large and similarly 

 formed. It connects posteriorly with the end of the valve and is supported by the 

 strong socket walls with which it is united. In Cr. siihelliptica at least its posterior 

 extremity is adnate to the floor of the valve for a short distance or even seems to be 

 mounted upon a short, low septum. It is deepl}' concave, and often with an 

 incomplete heart-shaped section. Usually it is divided by two radiating carinas into 

 three portions, only the central one having a homologue in Dielasnia. The shape is 

 pentagonal, the two antei'ior angles being formed by the two carina just mentioned, 

 which run out at the margin and project in the form of crura. The hinge plate 

 converges with the bottom of the valve posteriorly, the anterior extremity being 

 often a considei'able distance awa3^ The hinge plate is not divided in either Cr. 

 iowensis ox Cr. suhelliptica, as illustrated by Hall and Clarke's figures." I have not 

 been able to ascertain the characters of the loop in this species with satisfaction. It 

 seems to be short, with short diverging crura and short ascending lamellas. 



If we may rely upon Cr. ioioensis •^nA Cr. sitbelliptica as criteria, it seems to be 

 rather characteristic of this genus that the brachial valve is marked by rather strong 

 muscular impressions situated near together and anterior to the end of the hinge 

 plate. On internal casts three grooves, diverging anteriorlj', are usuallj- clearly 

 visible, inclosing the scars between their anterior ends. The central groove evi- 

 dently represents an incipient median septum, which in Cr. sahellip>tica at least is 



a Pal. New York, vol. 8, pt. 2, 1894, p. 297, fig. 215. 



