Geology and Paleontology. 725 
orders above named, which will be of much use to students. He 
admits three genera of Ichthyosauria, viz.: Ophthalmosaurus Seeley 
(Baptanodon Marsh), Ichthyosaurus Conyb, and Mizxosaurus Baur. 
He does not find any reason to subdivide the genus Ichthyosaurus. 
Of Plesiosauride he admits the genera Plesiosaurus, Thaumato- 
saurus, Pliosaurus, and Elasmosaurus (under the name Cimolia- 
saurus), but does not include in the last named the Jurassic species 
which have the same structure of the shoulder-girdle, which Seeley 
described under the name of Colymbosaurus several years ago. 
We find this course inconsistent, and believe the principles adopted 
by Seeley in his classification of the Plesiosauride to be well 
founded, except as to the genus Murenosaurus, which Mr. Lydek- 
ker shows to be a synonym of Colymbosaurus. Mr. Lydekker falls 
into the error of supposing that the genus Polycotylus is princi- 
pally characterized by the cupping of the vertebre. The fact is, 
that the structure of the paddles is as different from that of Plesio- 
saurus, as that of Ichthyosaurus is from Mixosaurus, and in much 
the same way. 7 
with most taxonomists, which we have stated elsewhere. We wi 
content ourselves now with observing that we find the method of 
Mr. Lydekker a matter of inconvenience rather than of convenience. 
We must also once more protest against being misquoted by Mr. 
ns 
pt. i., pl. ii. In this instance the head has been placed at the 
extremity of the tail,” ete., etc. On this I must observe that no 
such plate appears in the Transactions of the American Philoso- 
phical Society, or in those of any other Society. Of this Mr. 
Lydekker can easily satisfy himself. It is true, however, that an 
error got into the first descriptions of that species (see Proceed. 
Boston Society Nat. History, 1869-70), but it was done in 
imitation of the precedent laid down by the describer of the species 
named Cimoliasaurus (a name which Mr. Lydekker wishes to ach 
several years earlier. Here the cervical vertebre were descri 
as caudals. This mistake was corrected by its author after an 
inspection of the skeleton of Elasmosaurus. The plates and descrip- 
tions published by the American Philosophical Society are 
correct, and the genus Elasmosaurus is there for the first time 
fully characterized. The supposed genus Cimoliasaurus was never 
aracterized by the author of the name. 
