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GENEALOGY. 69 
Oxynoticeran Series. 
The apparently wide divergence from the usual structure of the Arietide 
presented by the hollow keel led me at first to classify this group as a distinct 
family. The close affinities with the Arietidee shown by the young, however, 
and the intermediate characters exhibited by the agassiceran series render such 
a classification unnatural and undesirable. 
The loss of the keel and flattening of the abdomen in the old has no parallel 
in the normal forms of the Arietide, so far as known It must be remem- 
bered, however, that this modification, together with its correlative decrease 
in the lateral diameter of the whorl, is a fulfilment of the series of geratologous 
transformations. 
First Subseries. — There are two subseries; one, the oxynotum subseries, with 
comparatively smooth shells, as in the less involute and stouter varieties of oayno- 
tum, and one, the Greenoughi subseries, which has highly developed folds. Both 
of these series progress in the amount of involution. The less involute Ozyn. 
oxynotum, the somewhat more involute Ozyn. Simpsoni2 and the still more involute 
Oxyn. Lymense of the first subseries are parallel with Ozyn. Greenoughi, Guibali, and 
Lotharingum of the second subseries. According to most authors, we could legiti- 
mately consider that the first three were only varieties of one species, though 
very few would be willing to join the last three under one specific name. The 
sutures of the adults of the oxynotum subseries are very close together, reminding 
one of the approximate sutures in the oldest stages of the individual in other 
genera. The pointed lobes and broad saddles, the short abdominal lobe and 
long finger-like marginal lobes and saddles, remind us also of the senile pecu- 
liarities of the sutures of Cor. trigonatum. The increase in number of auxiliary 
lobes and saddles and the general aspect of the sutures are, however, upon the 
whole additional complications, and therefore progressive characteristics. 
Second Subseries. — The gradations are uninterrupted from Greenoughi® to 
Lotharingum. The descriptions of the species show that the principal differences 
consist in the increasing involution of successive species, and a correlatively 
smoother and more compressed form of whorl. 
-The young of ozynotum and Greenough’ resemble closely the young of Agas. 
striaries. There are, however, no intermediate forms between the latter and 
these two species which would enable one to verify this relation of the younger 
stages. Whether Ozyn. orynotum or Agas. striaries gave rise to Oxyn. Greenoughi 
cannot be decided at present, owing to this deficiency in the evidence; but that 
both these forms came from the same common stock, and that this stock was 
Agas. striaries, seem quite probable. 
Oxyn. Guibali, the next species of this subseries, bridges the gap between 
Greenoughi and Lotharingum. .The nealogic characters of Oxyn. Lotharingum also 
show that this species must have been derived from Guibali. Lotharingum, like 
Ast. Collenoti and other terminal forms of series which have marked geratologous 
characters, is the smallest form of its own genetic line. 
1 Pl. x. figs. 24 and 31. - Sumi Ply ke ae. Lie 8 Summ. PI. xiii. fig. 13. 
