CONTRIBUTIONS TO PALEONTOLOGY. 



43 



described by Prof. Winchell, are not shown in the figure. These marks, 

 however, are shown in figs. G & 9, and characterize the ventral valves or 

 casts of this valve in all the known species of the genus. 



Fig. 8. 



Fig. 9. 



Fig. 10. 



Fig. 11. 



In the Fifteenth Report on the State Cabinet, I gave the accompanying 

 fig. 8 of the dorsal valve, and fig. 9 of the interior of a ventral valve. Figs. 

 10 & 11 are dorsal and profile views of Cryptonella exi?nia, from the Lower 

 Helderberg group, the earliest species of the genus known to me. 



The Genus Cryptonella may be characterized as follov^s : 



GENUS CRYPTONELLA (Hall, 1861). 



Shells terebratuliform, equilateral, inequivalve, elongate or 

 transverse, ovoid or sublenticular in form, without mesial fold 

 or sinus, or with these features very slightly developed towards 

 the base of the shell. Ventral valve with the beak extended or 

 incurved, and terminated by a circular foramen, which is li- 

 mited on the lower side by two small triangular deltidial pieces 

 (these are sometimes not visible externally, and the lower side 

 of the foramen is concealed by the umbo of the opposite valve). 

 Shell-structure finely punctate : surface marked by fine con- 

 centric strise, which are sometimes obsolete. Valves articulating 

 by teeth and sockets, the dental lamellae of the ventral valve 

 extending in thin vertical plates into the cavity of the valve. 

 The muscular impressions of the dorsal valve are strongly 

 marked above, and extend in two narrow, gradually widening 

 impressions, more than halfway to the base. The ventral valve 

 shows elongated muscular and vascular impressions below the 

 rostral cavity. 



In the dorsal valve, the hinge-plates, or bases of the crura, 

 support a slender loop, the two limbs of which are flattened, with 

 the faces vertical j and in its extension forward, the upper mar- 

 gins are inclined towards each other, gradually widening and 

 becoming conjoined in the centre, and thence extending forward, 



