234 : REVIEWS. 
species as a variety under the same name. If at the other end of the se- 
ries we should be permitted to add Ammonites Turneri, "as we think 
will perhaps prove to be merely a local variety of A. obtusu _ evi- 
den« 
typical Asteroceras obtusum, and in all respects it is similar to that spe- 
cies, differing only in the later or c production of the channels and 
keel and in its somewhat smaller 
A third opinion that all of icai were distinct species, may be answered 
first, by reference to the accelerations in the development of the pile oc- 
curring between the different individuals a the first variety, which in 
that case become types of varieties, and, o, by citing other species. 
Thes: one species of a lower genus perg incipiens, all the specimens 
of which are from one locality, fades by regular and inseparable grada- 
nels 
farther be strengthened by showing that this via or absence of chan- 
nels becomes in the Middle Lias of such importance that it constitutes a 
Discoceratide (Arietes). Thus Hildoceras thle: en and Wal- 
cottii) differs from Grammoceras ene striatulus, Amm. Aalense, etc.) 
principally in these characteristics 
he presence or absence of eee: therefore, or any change of form 
to which the abdomen may be subjected, cannot, to use the terms of the 
modern systematist, be considered as of slight importance even though 
we find them, when first introduced, subject to simple varietal changes in 
some species 
he Iais of a review do not permit us to continue this part of the 
subject. Lenie many similar instances, therefore, to a in due: 
group. 
marks which refer to the possibility of determining beforehand the future 
course of the changes of a group, but have been accidentally passed over 
in silence by him. He has also given Professor Cope the undivided credit 
move all doubt that the aim of a large part of the investigations there 
Bulletin of the Museum of C 'ative Zoology, No. 5, p. 99. 
