Reviews—Dr. Geo. Baur—Ichthyopterygia. 329 
T]I.—On rue MorpHonocy AnD ORIGIN oF THE ICHTHYOPTERYGIA.' 
By Dr. Grore Baur, Yale College Museum. 
HE present paper is one of the results of Dr. Baur’s recent tour 
in Europe, during which he was enabled to examine the Fossil 
Vertebrata in most of the principal Museums of the Continent and 
England. The various known characters of the Ichthyopterygian 
skeleton are reviewed and compared especially with the existing 
Sphenodon; and the conclusion is arrived at, that these Mesozoic 
marine reptiles bear the same relation to certain ancestral terrestrial 
Rhynchocephalia, that is apparently borne by the living Cetacea to 
early ungulate Mammalia. The skull is only comparable with that 
of the Rhynchocephalia (especially Sphenodon) and the Lacertilia. 
The only real difference is that, as in the Cetacea, the facial portion 
has been very much elongated. ‘The general structure of the skull 
resembles that of the Dolphins: in its morphology, it is a copy of 
the Sphenodon skull.” Most of the accepted interpretations of the 
cranial bones are adopted, but a correction is offered in regard to the 
large bone forming the postero-external boundary of the supra- 
temporal fossa. This is determined to be the supratemporal element 
of the Lacertilia, and in Sphenodon is said to be united with the 
squamosal; the bone in Ichthyosaurus has been termed mastoid by 
Owen, and squamosal by Seeley and Cope. Between this element, 
the postfrontal, postorbital, quadratojugal, and quadrate, is articu- 
lated the true squamosal, named prosquamosal by Owen, and supra- 
quadrate by Seeley. 
After the detailed comparisons, Dr. Baur proceeds to discuss the 
morphology of the Ichthyosaurian paddle. The most primitive 
example known is that of Ichthyosaurus cornalianus, Bassani, from 
the Trias of Besano, Italy, which is placed in a new genus, 
Mixosaurus. The radius and ulna are elongated bones, with a 
considerable intervening space. The paddle of Baptanodon or 
Sauranodon is regarded as the most specialized form, and the bone 
termed by Marsh “intermedium ” is interpreted as ulna, while the 
so-called “ulna” is held as probably representing the pisiforme. 
The oldest Ichthyopterygia had few phalanges and not more than 
five digits; later, through the adaptation to the water, the number 
of phalanges increased, ‘and more digits appeared, chiefly by division 
of the former, but sometimes by new formation on the ulna side. 
An interesting analogous case is noted in the manus of a Manatee, in 
which Dr. Gadow has observed an exceptional increase of the 
phalanges beyond the normal Mammalian to the number of three. 
In conclusion, Dr. Baur proposes the following classification of 
the Ichthyopterygia :— 
Group A. Radius and ulna elongated, separated by a space in 
the middle. Teeth of two forms, but not so numerous as in the 
Ichthyosauride. Small animals. Triassic. 
Family, Mixosauride, Baur. Genus, Mixosaurus, Baur. 
Group B. Radius and ulna short bones, touching each other. 
Teeth well developed and numerous. 
1 American Naturalist, 1887, pp. 837-840. 
