The Suhgeneric Groups of Naticopsis. — Kcyes. 195 
cies //. ( fsonema) depressa M. it W. Loxonema bellulata Hall 
was also included ; and later Meek ' added another congen- 
eric form — Isonema humilis. In 1873 Hall and Whitfield' 
figured /. huniilis as Naticopsis Icevis Meek ; the specimen, 
however, was very perfect and exhihited all the generic 
features much more clearly than the type oi Isofie ma. Subse- 
quently Meek," redefining his /. humilis placed both this 
species and /. depressa subgenerically under Naticopsis. Six 
years later Hall ' made Loxonema bellulata[^ Isonema hellulata 
(Hall) M. cfe W.] the type of a new genus — Callpnema, which 
also embraced two additional forms — one originally described 
as a Pleurotomaria and the other as a Plati/stoma. Callone- 
ma as thus understood bears only a slight superficial resem- 
blance to the palicozoic Naticida?, and probably does not 
belong to this family. The two forms that constitute the 
"Isonema" group are slightly more depressed than the shells 
of Naticopsis generally ; and have the small costfc that ex- 
teiul a short distance from the sutural line, more lengthened 
Explanation of kicl-res. — Fi^- 1. Naticopsis phillivsi McCoy. Fig. 2. 
Trachyditmia whederi Swallow, enlarged two uiameters. Fig. 3. 
Naticopsis ventricosa N. & P. Fig. 4. N. (Igonenui) humilit Meek. 
Proc. .\cad. Nat. Sci., Phila., 1871, p 
'2.Srd Kept. State Cab. N. Y.,pl. .\n. 
Pala'. Ohio, vol. i, p. 214. 
Paho. N. Y., vol. u, p. 50. 
