CONTRIBUTIONS TO PALAEONTOLOGY. 47 



Fig. 18. Fig. 19. Fig. 20. Fig. 21. 



From the data here given, it will be seen that the G-enus Cryptonella 

 is nearly related to Centronella, though both may perhaps be regarded 

 by some palaeontologists as of only subgeneric value, differing as much from 

 each other as the former does from Renssel^ria, or as Terebratula 

 from Terebratulina or Waldheimia.* 



* After the preceding observations had been written and print- Centronella 

 ed,* I received from Dr. Rominger a drawing of the interior of glans-fagea.\ 

 the Centronella glans-fagea, which has been copied in the accom- 

 panying figure, and was likewise inserted in the supplementary 

 note to the paper referred to above. 



SiDce that time I have examined, and have now before me, the 

 specimens of Dr. Romingbr; and I can have no hesitation in 

 pronouncing them identical with typical specimens of the C. 

 glans-fagea. It is possible that some closely allied form may 

 present the peculiarities of the loop illustrated by Mr. Billings; but it seems 

 probably due to imperfection of the specimens, or displacement of the parts. At a 

 later period (May 1861), Mr.B. has published Centronella hecate; giving, in one 

 of his illustrations (figure 99 a), "A specimen with the dorsal valve removed, 

 ** showing the loop, which is covered with minute crystals of silex." Since no 

 mention is made of any differences observed between the loop of this species and 

 that published in 1859, we may presume it to have been similar. 



In my former paper, I have expressed some hesitation in regard to placing those 

 forms which I had referred to Cryptonella, in the Genus Centronella;J but 

 after a careful examination of specimens of C. glans-fagea, showing the internal 

 loop, I shall venture to suggest the merging of the Genera Centronella and 

 Cryptonella into one, retaining the former name whicl! has precedence in time. 



* Transactions of the Albany Institute, Vol. iv, February 1863. 

 t Interior, showing the loop, from a figure by Dr. C. Rominger. 



$ '' We are therefore scarcely warranted in placing in the Genus Centronella, 

 species having an internal organization so different as that observed in species of au- 

 thentic Cryptonella, until a reexamination of the original specimens of Mr. Billings 

 shall confirm his first observations, or show them to correspond with those of the genus 

 last named " ( Transactions Albany Institute, Vol. iv). 



