.33,. ICHTHYOSAURIAN REPTILES. 519 



/. longifrons, is only a variety of this species, an opinion with which 

 we are much disposed to concur. 



Much important information is furnished by Dr. Fraas with 

 regard to certain Ichthyosaurs of the Continental Upper Lias, 

 described by Theodori in 1854, which it has hitherto been impossible 

 for English writers to refer to their proper systematic position. The 

 first of these is Ichlhyosaiirus crassicostatus, which is now shown to be 

 allied to /. teniiirostris, although having a much shorter snout. It has, 

 therefore, the same relation to the latter as is presented by the so- 

 called /. bvevirostvis to /. communis of the English Lower Lias. We 

 are, however, by no means assured that such short-snouted forms — 

 which, be it observed, are of extreme rarity — are anything more than 

 abnormal examples of the longer-snouted species to which they are 

 severally allied, similar abnormalities being well-known to occur 

 among the Cetacea. Then, again, we have the still more rare /. 

 macvophthalmiis, which appears to differ from the type of /. crassicostatus 

 only by its larger orbits, smaller teeth, thinner ribs, and the absence 

 of slits in the bones of the paddles. In respect to its teeth, this form 

 serves, indeed, to connect /. trassicostatus with /. qiiadviscissus, and it 

 thus appears to us to require much stronger evidence than any 3'et 

 published to prove that these three forms are really specifically 

 distinct. 



The third of these hitherto imperfectly known Upper Liassic forms 

 is /. ingeiis, which is now definitely referred to the Tenuirostrine group, 

 and appears to be mainly characterised by its gigantic size. In this 

 respect it, however, scarcely exceeds the type of /. zetlandiciis ; and 

 we see no reason why it should not be specifically the same, in 

 which case Theodori's name would have to be retained. More- 

 over, if this form be identical with /. zetlandiciis, and the latter with 

 /. guadriscissns, the name /. ingens antedates both the others ; the 

 same being the case with regard to the names /. crassicaudatus 

 and /. macrophthahnus. 



Before leaving the Upper Liassic Ichthyosaurs of the Tenuiros- 

 trine group, we must briefly refer to the paper by Professor Gaudry, 

 quoted at the end of this review. This refers to a large Ichthyosaur 

 discovered in the Upper Lias of the Yonne, and provisionally named 

 /. biirgnndicT. It is described as having a long snout, with a pectoral 

 limb of the type obtaining in the Tenuirostrine group, and the teeth 

 fluted. The pelvic limb is, however, peculiar, in that it has two rows 

 of bones arising from the intermedium, or median bone of the tarsus, 

 after the fashion obtaining in /. communis ; and it appears to be this 

 character which led Professor Gaudry to consider the specimen as 

 indicating a new species. We would suggest, however, that such a 

 peculiarity may perfectly well be an individual one, in which event 

 we fail to see that the other point's mentioned in the description are 

 sufficient to distinguish this skeleton from /. zetlandiciis. The speci- 

 men is, however, of considerable interest, as showing how species 



