5i8 NATURAL SCIENCE. s^p^.., 



are aware, all the skeletons with fcetuses belong to one single species ; 

 thus suggesting that this particular species was alone viviparous. 

 Dr. Fraas considers that the retention of the ova within the body of 

 the parent until developed into fcetuses of considerable size, is to be 

 accounted for by the purely marine mode of life of these reptiles, 

 which he believes were not in the habit of visiting the shore. If it 

 should prove that viviparous reproduction was confined to the species 

 with narrow paddles, like the one represented in our figure, it may be 

 suggested that the species with broad paddles, like /. covununis of the 

 Lower Lias, were accustomed to visit the land to deposit their eggs, 

 and thus had no need of special arrangements in regard to their 

 reproduction. 



Coming to the systematic portion of the memoir, we find, as 

 might have been expected, that the small Ichthyosaur from the 

 German Trias, described as Ichthyosanrns atavits, is transferred by 

 Dr. Fraas to the genus Mixosaunis, originally founded upon the 

 evidence of specimens from the Italian Trias. This genus, it may 

 be observed, in the structure of its limbs, tends to bridge the gap 

 between the true Ichthyosaurs of the Lias and more normal 

 reptiles ; and it is regarded by Dr. Fraas as the proximate ancestor 

 of the two great groups of Ichthyosaurs, namely, those with narrow 

 and those with broad paddles. Of the Ichthyosaurs of the Lower 

 Lias, Dr. Fraas has but little to say, since they are but poorly 

 represented in Germany, We may observe, however, that it has 

 been shown in the " Catalogue of the Dublin Museum," standing 

 sixth on our list, that the long-snouted forms described as 

 /. tenuirostris and /. latifrons, really belong to but a single species, 

 for which the former name must be employed. From our own studies 

 we also fail to find satisfactory means of distinguishing the long- 

 snouted Ichthyosaurs of the Upper Lias from the Lower Liassic 

 species, and we are, therefore, fain to regard the three species, 

 /. tenuirostris, latifrons, and loiigirostris, admitted by Dr. Fraas, as 

 founded upon one and the same form. Our readers desirous of further 

 information on this species may refer to the paper standing last on 

 our list. 



The great bulk of the descriptive portion of Dr. Fraas' memoir 

 relates to the Ichthyosaurs of the Upper Lias, the skeletons of which 

 are found so beautifully preserved in the shales of Holzmaden. For 

 the common German species (the one represented in our figures) the 

 name Ichthyosaurus quadriscissus (in allusion to the slits in the edges of 

 the bones of the front of the paddles) is adopted ; and, on the whole, 

 we think this is the best course, seeing that our author has shown 

 that /. acutirostris, with which this species had been identified, is a 

 totally distinct form. This species is represented in the Upper Lias 

 of England as well as Germany; and Dr. Fraas is disposed to consider 

 that the huge English Ichthyosaur, described as /. zetlandicus, 

 together with an identical form from Normandy, figured as 



