C. D. Walcott — Paleozoic Pteropods. 21 



to become deciduous in many instances, and we now find nu- 

 merous examples showing the blunt terminal portion. Some 

 shells show the rounded, smooth end without any constric- 

 tion ; others have a narrow concentric constriction just within 

 the termination. The cast of the surface of the septum shows 

 a slight central cicatrix or scar, but no evidence of a perforation 

 in the septum could be observed. The average size of the 

 tube, at the point of decollation, is l mm . The largest seen is 

 l-5 mm and the smallest -75 mm . 



When studying the septum, the close similarity between it 

 and that of the first septum of the species of Orthoceras and 

 Cytoceras, as figured by Barrande (Cephalopodes, Etudes gene- 

 rales, 1877, pis. 487, 488), were, at once, brought to mind, and 

 also the interesting question of the relations of these shells to 

 the cephalopoda. 



Since the above was written I have received a paper from 

 Mr. Gr. F. Matthew, in which he states that several of the 

 Pteropod shells, from the base of the St. John group, have 

 several distinct septa at the base of the tube. The genus and 

 species is not mentioned (Nat. Hist. Soc. N. B. Bull., 10, p. 102, 

 1885). 



Mr. Matthew quotes, in the same paper, from a letter written 

 by Mr. Alpheus Hyatt, where the latter says : " These fossils 

 with their distinct septa are startlingly similar to certain forms 

 of Nautiloidea, but there is no siphon. They, however, confirm 

 Yon Jhernig's and my opinion that Orthoceratites and Ptero- 

 pods have had a common, but as yet undiscovered, ancestor in 

 ancient times." 



In a letter dated April 9, 1885, Mr. Matthew states that he 

 has several species of the Hyolithellidas from the St. John 

 Group that have several septa toward the apex of the tube for 

 which he has proposed two generic divisions, one of which he 

 calls Camarotheca ; this will probably include H. Emmonsi, 

 and I have used the name in a subgeneric sense, until I can 

 learn more of the character of the septa of H. Emmonsi. 



A single specimen of H. primordialis, from the Potsdam 

 sandstone of Wisconsin, also shows evidence of a transverse 

 septum. 



Note op Correction. — In describing the figures accompanying the article on 

 Linnarssonia (this Journal, vol. xxix, February, 1885, p. 117), figs. 1 and 2 are 

 given as those of Obolella chromatica, and credited to Mr. Billings. The artist, in 

 preparing the figures, copied, by mistake, those of Obolella crassa Ford. The fact 

 escaped my notice at the time, and I unintentionally credited Mr. Billings wit? 

 figures that had been published by Mr. S. W. Ford. c. d. w. 



