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included under this name. One is separated above as Tarphyceras 

 Farnsworthi and the other below as Aphetoceras attenuatum. The 

 type is that figured by Billings, and this had the living chamber 

 free and deviating strongly from the spiral. It was 91 mm. long 

 on the dorsal surface and more than one-half of a volution in 

 length when this measurement was applied to the coil of the preced- 

 ing whorls. The siphuncle in the ephebic stage was propioventran 

 and the septa much closer together than is usual in this genus. 



Aphetoceras attenuatum. 



Lituites Farnsworthi, Bill, {pars.) (op. cit., p. 21). 

 Loc, Phillipsburg. 



This species is founded upon the specimen described by Billings 

 on p. 21 of his Paleozoic Fossils as having first two whorls in con- 

 tact and making a coil an inch across. These whorls are, however, 

 not in contact on his specimen, if my drawing of this is correct. 

 The specimen is of nearly the same size as the type of Aphetoceras 

 Farnsworthi, but one and a quarter volutions are free, so as to 

 leave a gap of 8 mm. before the completion of the first quarter of 

 the septate part of the eccentric volution, and at the end of the 

 same this gap has increased to 13 mm., and in the next quarter, at 

 the end of the living chamber, it is 25 mm. The departure of the 

 free whorl of Farnsworthi increases, as shown in Billings' drawing, 

 in less than one-half of a volution to 40 mm. 



The septate part of the eccentric volution in this specimen is 

 58 mm. long, the living chamber is 88 mm. long. The former 

 would occupy about three-fourths of a volution if it followed a reg- 

 ular open spiral curve, and the latter would be about one-half of a 

 volution, estimated in the same way. 



The septa are similar to those of Farnsworthi. The fragment of 

 the siphuncle observable in the neanic stage changes in the length 

 of 10 mm. from nearly subventran to propioventran. 



Deltoceras* n. g. 



The shells of this group resemble those of Aphetoceras, but are 

 just one grade more complicated. The whorls are similar in section, 

 but grow more rapidly in the ventro-dorsal diameters, the siphuncles 

 in some species are very large and ventral. The sutures are simi- 



* A(Xto$. a scroll. 



