R. Lydekker—WNote on the Ichthyopterygia. 309 
VI.—Nore on run CLAssrricATION OF THE ICHTHYOPTERYGIA (WITH 
A Notice or Two New Sprcizs). 
By R. Lyprexxer, B.A., F.G.S., ete. 
|S levee devoted several weeks to the study of the magnificent 
collection of the remains of Ichthyopterygians preserved in 
the British Museum (Natural History), I purpose on this occasion to 
give a brief notice of some of the conclusions at which I have arrived, 
since a considerable interval will elapse before the publication of that 
part of the Museum “Catalogue of Fossil Reptilia” in which my 
observations will be more fully recorded. 
Exclusive of the genus Cetarthrosaurus, which is referred by Mr. 
Hulke to the Mosasauridea, four genera of Ichthyopterygia have hitherto 
been described; viz. Ophthalmosaurus, Seeley, Baptanodon (Sauran- 
odon), Marsh, Ichthyosaurus, Konig, and Mixosaurus, Baur. Since, 
however, there appear to be no characters by which Baptanodon can be 
generically separated from Ophthalmosaurus, I am inclined to follow 
the suggestion made by Dr. Baur, and unite the two; thus reducing the 
number of genera to three. With regard to Ichthyosaurus, it has been 
suggested by more than one writer that this genus is susceptible of 
division into two or more genera; and there is much to be said for this 
view, since there is an extraordinary amount of structural difference 
between many of the forms. If, however, the species be arranged 
in their natural relationship, which corresponds to a great extent 
with their distribution in time, it will be found that these distinctive 
characters tend to shade more or less completely into one another. 
Since, moreover, the skulls of all the species seem to be so nearly alike 
in general structure that it is very improbable that good generic 
characters could be drawn from them, I have come to the conclusion 
that it will be more convenient to the paleontologist, and most 
certainly to the pure geologist, to retain the genus in its original 
wide sense. I intentionally use the term convenient in this con- 
junction because I am glad to see that Prof. Flower,’ in his recently 
published memoir on the Liberian Hippopotamus, has expressed his 
opinion very clearly that the restriction or multiplication of generic 
terms is purely and simply a matter of convenience; and that their 
multiplication rather tends to make us lose sight of the mutual 
relationship of allied forms. I am further convinced of the advisa- 
bility of retaining the original use of the term Ichthyosaurus, because 
if we once begin to subdivide it, it will be almost impossible to 
know where to stop. 
Dr. Baur, who adopts the view of the advisability of splitting up 
the type genus, makes the three above-mentioned genera the types of 
three distinct families ; but if the term Ichthyosawrus be employed in 
the sense indicated above, it appears to me that the whole three 
genera may be conveniently included in asingle family—the Ichthyo- 
sauride. 
The last-mentioned writer has shown very clearly that while 
Ichthyosawrus occupies the middle position, Ophthalmosaurus is the 
1 P.Z.8. 1887, p. 614. 
