196 REPORT ON THE STATE CABINET. 



valve extending downwards into the cavity of the shell. The muscular 

 impressions in the dorsal valve are strongly marked above, and extend 

 in two narrow separated impressions more than halfway to the front 

 of the shell : the ventral cast shows elongated muscular and vascular 

 impressions. 



The species of this genus are more elongate than Merista and Meris- 

 TELLA, and those now known are less distinctly marked by mesial fold 

 and sinus ; while the beak is more attenuate, often a little flattened, and 

 i^arely so closely incurved, as in the genera cited. The punctate struc- 

 ture of the shell is a distinguishing character. 



This genus was first described as above cited, and figures of the 

 exterior form and of the interior of the valves were given in the 

 Fifteenth Report. The results of some farther investigations were given 

 in the Sixteenth Report, and an illustration of what was supposed to be 

 the internal appendages of the shell. Al^out the same time it was 

 discovered that some punctate shells of the same general form possessed 

 the loop of Terebratula proper ; and it became a matter of great interest, 

 and still greater difficulty, to determine the internal structure of the 

 species. I had referred to this genus the Terebratula lens^ T. UncMceni, 

 T. rectirostra and T. planirostra, species described in a preceding report. 

 Having ascertained that the internal loop in Centronella glans-fagea is 

 essentially similar to that of C. julia (Winchell), a species having the 

 external form of Cryptonella, I supposed it possible that the two genera 

 might be merged into one. Since that time, I am not aware that any 

 farther investigations have been made, tending to throw light upon this 

 subject. 



It has therefore appeared to me very desirable to learn, if possible, the 

 internal structure of any one of those species which I originally referred 

 to the Genus Cryptonella. Of two of these, C. rectirostra and C. j^lani- 

 rostra, I have fortunately been able to obtain an exposition of the form 

 and structure of the loop, as will be shown in the illustrations of the 

 species. 



The crura have the general form of those in Waldheimia, extending 

 in a long recurved loop, with long processes descending into the ventral 

 valve, between which and the apex of the shell the crura are united by 

 a transverse, band, differing in this respect from that genus, while the 

 muscular impression and extended beak offer other distinctions. 



I have thought it desirable, therefore, to continue the name Crypto- 

 nella to include these two authentic species ; while the other two species 

 are included under it from their general form. 



