IV. 



Recent Advances in Knowleclo'e of the 

 Iclithyosaiirian Reptiles. 



"PROM the circumstance that nearly all their skeletons found in the 

 -*- English Lias have a dislocation in the vertebrae of the tail, Sir 

 Richard Owen was led many years ago to the conclusion that the 

 extinct marine reptiles, known as Ichthyosaurs, were furnished with 

 an expanded fin at the end of the tail, and that the weight of this fin 

 caused the fracture in question. Years passed on without affording 

 any evidence one way or the other in relation to this bold theory ; but 

 at length, in the present year, there has been discovered in the Lias 

 • of Wiirttemberg the skeleton of one of these reptiles, in which the 

 outline of the fleshy parts is completely preserved, and which proves 

 the existence of a caudal fin of still larger dimensions than Owen 

 supposed to be the case. This interesting specimen is described by 

 Dr. E. Fraas in the paper standing fourth in our list, from which the 

 accompanying figures are reproduced. We already knew that in the 

 paddles the fleshy part was extended much behind the bony skeleton; 

 but the new specimen shows us that, in addition to the tail-fin, the 

 Ichthyosaurs had a triangular fin on the middle of the back, behind 

 wliich was a crest of horny excrescences compared to those of 

 the crested newt. The tail-fin is vertical and nearly symmetrical 

 externally, although the backbone runs downward to terminate in its 

 lower lobe. In this respect the fin has the same general aspect as in 

 the Sharks, except that in the latter the backbone runs into the upper 

 lobe. It shows, indeed, as Dr. Fraas remarks, how closely analogous 

 is the form of Ichthyosaurs to fishes ; and it thus further justifies 

 the title of " fish-lizards " which has been applied to these reptiles. 



An exhaustive comparison of the skeletons of the Ichthyosaurs 

 from the Liassic deposits of the Continent with those from the corre- 

 sponding horizons of England, has long been a desideratum. This 

 want has, however, now been remedied by Dr. Fraas, in the magni- 

 ficent work mentioned second in the following list. By no means 

 the least important features in that work are the beauty, number, and 

 large size of the plates with which it is illustrated ; and with these by 

 his side the English Paleontologist ought no longer to have much 



