447 
from the species figured either by Dewitz or Schréder. In fact, the 
figures show that there are very likely three species under this one 
name. 
This genus is described here partly because it is an excellent illus- 
tration of the correlation of the dorsal and ventral saddles with 
elliptical compressed whorls and gibbous abdomens and gibbous 
dorsal sides such as occur in many cyrtoceran and gyroceran forms, 
and also because of its resemblance to Aphetoceras. 
Aphetoceras,* n. g. 
The shells of this genus are remarkable for their resemblances, 
until a late stage of growth, to the cyrtoceran genus, Melonoceras, 
from which they differ in having open apertures, and in this case 
they would probably compare more closely in these stages with 
Oonoceras. These shells are, however, coiled with an even gyro- 
ceran curvature that does not bring the whorls in contact at any 
stage. 
The form of the whorl in section is compressed elliptical or ovi- 
form, the venter narrower than the dorsum. This outline is com- 
mon to all of the epembryonic stages as far as known. ‘The nepi- 
onic substage has, however, not been seen as yet. 
There is no impressed zone at any stage. 
The whorl probably deviates from the spiral in the paragerontic 
substage, but this has not been observed, unless Farnsworthi is a 
true member of this generic phylum. 
The shell is invariably smooth so far as kno-yn. 
The sutures have very nearly the same form throughout the epem- 
bryonic stages, so far as known, having dorsal and ventral saddles 
and broad lateral lobes in correlation with gyroceran characters of 
the coil. 
The siphuncle is subventran or propioventran and probably does 
not vary much from these positions in any species. 
This genus is separable from Planctoceras by the gyroceran mode 
of coiling, by the form of the whorl in section, by the length of 
the living chamber and position of the siphuncle. 
APHETOCERAS AMERICANUM, 0. s. (Pl. vi, Figs. 5-8, > %4). 
Loc., Port au Choix, Newfoundland. 
This shell has an open gyroceran coil and, so far as could be 
* Avertds, free. 
