118 MEMOIRS OF THE CARNEGIE MUSEUM 
The left orbit of the same specimen has the ring nearly circular (see PI. X., fig. 2) 
and the plates quite flat, though as Frass has pointed out in life they were probably 
arranged at somewhat more of an angle. It might be well to mention here that the 
sclerotic ring in the skull of 1955” (B. discus) shows the same flat circular arrange- 
ment of the plates observed among most of the members of the Ichthyosauria. 
The specific characters given by Marsh for separating the two species of Baptano- 
don are quite as superficial as the generic characters just reviewed. Size alone is the 
only difference of importance, but as in most reptiles these probably continued to 
grow throughout life. ‘The breadth of paddles,” “ elongation of the facial portion 
of the skull,” “slender snout,” etc., are illusionary characters and would not serve 
to distinguish the two species. For example in giving the distinguishing characters 
between B. discus and B. natans (type of the genus) Marsh says: ‘The paddles, also 
are broader in proportion to their size, than in the type species.” It is now definitely 
understood that the extremities of B. natans areunknown. Howeverin the Catalogue 
of Fossil Reptilia and Amphibia in the British Museum, fig. 5, p. 7, is a figure of 
the left pelvic limb of B. natans (after Marsh from the Proc. Geol. Society). The 
illustration shows the dorsal surface of the limb and is to all intents the reverse 
view of the left pelvic (?) limb of B. discus and accidentally referred to the wrong 
species. 
In a more recent paper™ the late Dr. W. C. Knight has added much to our knowl- 
edge of Baptanodon besides giving reasons for considering this genus distinct from 
Ophthalmosaurus. 
To correct some inaccuracies in the characters enumerated I will take up the 
arguments advanced by him and make such comments as access to literature and 
more complete and better preserved material render possible. 
They are as follows: 
“In comparing the limbs of 1. The absolute length of limb in 
Ophthalmosaurus and Baptanodon one either form apparently unknown, but 
should consider the following points : in so far as one may judge from illus- 
1. In Baptanodon the humerus is trations the limbs of the two forms ap- 
about one third the length of the limb.” pear to have about the same propor- 
tions. Lydekker in the catalogue of 
Fossil Reptilia and Amphibia in the 
British Museum gives measurements of 
53 Nicholoson and Lydekker have the same illustration in their ‘‘ Manual of Paleontology,’’ Vol. II., Fig. 1034, and 
ascribed to the same species, though (after Marsh and Hulke). 
54 Knight, W.C., ‘‘Some Notes on the Genus Baptanodon with a Description of a New Species,’’ Amer. Jour. Sci. (4) 
Vol. XV. 
