166 
NATJTILOIDEA, 
This description of Solenocheilus was afterwards emended by Hyatt 
in the Proceed. Boston Soc. Nat. Hist. vol. xxii. p. 296, and he there 
restores the name Asymptocems^ proposed by Byckholt, making 
Solenocheilus a synonym. I have stated further on why the name 
Asymptoceras cannot be retained. Hyatt thus describes the group 
now under discussion : — “ The whorls increase very rapidly in size, 
the living chambers are short, with flaring \i. e. spreading outward] 
or slightly contracted apertures. The venter [periphery] is flattened, 
Fig. 27. 
Solenocheilus dorsalis. — a, lateral yiew ; h, front view ; the inner whorls are 
slightly distorted. Drawn from Phillips’s type specimen in the “ Gilbert- 
son Collection.” About one half natural size. 
or slightly hollow along the centre. The sides are more or less 
gibbous, and the umbilical shoulders project in heavy ridges, or a 
large pair of tubercles. Upon each side of these are flutes [channels] 
which are specially characteristic. The dorsum is also remarkable 
for having the centre gibbous as in Gyroceran forms, indicating the 
recent derivation of the genus from more loosely coiled forms. The 
sutures have broad ventral lobes, saddles at the abdominal [peri- 
pheral] ridges, broad lateral lobes, saddles at the umbilical shoulders 
and dorsal lobes, with small annular lobes [= internal or dorsal 
lobes]. Siphon near the venter [= ventral or peripheral margin]. 
.... The presence of a pair of large tubercles on the chambers of 
habitation in some of the species unites them with such forms as 
Asymp. (^Naut.') bifrons., sp., de Kon. Calc. Garb. pi. 16 
(Solenocheilus) pentagonus.^ J. Sow. sp.]. Even the contracted 
