520 NATURAL SCIENCE. 



with narrow paddles (Longipinnate) may have passed into those in 

 which the paddles were wide [Latipinnate). 



With Ichthyosaurus acutiyostvis we come to the first of those 

 species in which the teeth, instead of being evenly fluted all round, 

 are smooth, and carry two or three sharp vertical ridges ; from which 

 character the members of this group have been separated from the 

 genus Ichthyosaunis as Temnodontosaurus. Dr. Fraas has rendered good 

 service in showing that /. acutivostvis is a member of this group, and 

 consequently has nothing to do with /. qiiadviscissus, with which it had 

 been erroneously identified. The only other Upper Liassic species 

 mentioned is the gigantic /. tvigoiiodon — the analogue of the still 

 more gigantic /. platyodon so commonly found in the Lower Lias 

 of England. 



Of the post-Liassic species of the Jura, the materials at Dr. 

 Fraas' command do not appear to have been very abundant. It is, 

 however, considered that the Jurassic /. leptospondylus is an ancestral 

 type of the genus Ophthalmosaums, characterised by having three 

 bones articulating with the humerus, and being evidently the extreme 

 modification of the Latipinnate type ; a further characteristic being 

 the tendency to a partial or complete loss of the teeth. On the 

 other hand, our author is indisposed to admit the reference of the 

 well-known Cretaceous /. campylodon to the Latipinnate group, and 

 rather considers that this powerfully-toothed species has been 

 derived from the Longipinnate group, which is not regarded as the 

 ancestral stock of the Latipinnates. The main ground of this new 

 departure appears to be the alleged resemblance in the structure of 

 the skull of /. campylodon to that of the Longipinnates, as displayed 

 in sections. No explanation is, however, offered to account, on this 

 view, for the resemblance of the radius of the Cretaceous species to 

 that of the Latipinnates, and its dissimilarity to the corresponding 

 bone of the Longipinnates. Some day, perhaps, we may have the 

 good fortune to obtain an entire paddle of Ichthyosaurus campylodon, by 

 which the question will be decided finally. With a brief reference to 

 Professor Capellini's memoir, recording the occurrence of this widely- 

 spread species in the Cretaceous of Italy, we may appropriately bring 

 to a close our survey of these important series of contributions to our 

 knowledge of the Ichthyosaurs. 



REFERENCES. 



1. Capellini, G. — Ichthyosaurus campylodon nelle Argille Scagliose dell' Emilia. 



Mem. Accad. 1st. Bologna, ser. 4, vol. x., pp. 431-450, pi. i., 1S90. 



2. Fraas, E. — Die Ichthyosaurier der Siiddeutschen Trias- und Jura- 



Ablagerungen 410, Tiibingen, i8gi, pp. 81, pis. xiv. 



3. Ichthyosaunis numismalis. Jahreshefte Vtreins vat. Nat. IVihtt., 1892, pp. 



22-31, pi. i. 



4. Uebereinen neuenFundvon/c/j^/ijosflKH/s in Wiirttemberg, Neites Jahrbuch 



f. Mineralogic, 1892, vol. ii., pp. 87-go. 



