50 PALAEONTOLOGY OF NEW YORK. 



CALLONEMA, n. gen. 



Shell subglobose, turbinate or ovoid-conical. Volutions rounded or sometimes 

 subangular above and below ; outer lip apparently thin ; columellar lip 

 thickened and spreading over the volution above and extended below; 

 axis ombilicate. 

 Surface marked by fine even striae which extend equally over the volutions, 

 rarely divided, and sometimes merging into the ordinary striae of growth, 

 and extending into the umbilicus. 

 This generic name is proposed to include such forms as Isonema bellatula, 

 Isonema Lichas (if these two prove distinct), Pleurotomaria {Isonema) imitator, and 

 similar forms; the chief external characters being the sharply elevated, even, 

 thread-like concentric striae traversing the volutions above and below, a distinct 

 columellar lip, and an umbilicate axis. 



I had accepted, without critical examination, the determination of Mr. Meek 

 (Mkf.k & Worthen), referring Loxonema bellatula to the genus Isonema; but while 

 this volume is passing through the press, a comparison of the generic descrip- 

 tion and the characteristic figure of the type species (/. depressa), shows that this 

 reference cannot be sustained. The generic description of Isonema is as follows : 



" Shell depressed subglobose, turbinate, or conical-subovate, obtusely angular 

 around the middle of the body-whorl. Aperture subrhombic ; outer lip thin, 

 entire; inner lip a little flattened or impressed in the umbilical region, appar- 

 ently for the support of an operculum, very thin, or scarcely continuous above; 

 axis imperforate. Surface ornamented with transverse, very regular lines on 

 the upper side of the volutions. 



In 1865 we proposed the name Isonema for this type, as a subgenus under 

 Holopea. Farther comparisons, however, have since led us to regard it as 

 generically distinct from Holopea, from which it differs in its angular instead 

 of rounded volutions, as well as in its imperforate axis, flattened inner lip, 

 rhombic instead of rounded aperture, and strong regular lines of growth. 

 From I'l.numuMAUiA it will he at once distinguished by its entire lip, and the 

 absence of a revolving band on the whorl. From Cyclonema it differs, in being 

 entirely without the characteristic revolving lines of that genus, and marked 

 by strong transverse stria'. 



In addition to the typical species here described, this genus includes 

 I. bi'lli/tula (Loxonema bellatula, Hall: Fifteenth Report Regents Univ. N. Y., 

 p. 103, figs. 4 and 5)."— Geol. Survey of Illinois, Vol. Ill, pp. 442, 443. 1868. 



