138 Dr. B. Dean — Fishes, Living and Fossil. 



lozenge-shaped denticles, and was everywhere lacking in membrane- 

 bones. The lateral line retained its groove-like character." 



Cladoselache is the type of a new order, Plenropterygii, and that 

 of Acanthodii immediately follows in Dr. Dean's classification. We 

 do not agree with this association, hut there is perhaps much reason 

 for differences of opinion in the present state of knowledge of the 

 endoskeleton of all these early Palasozoic fishes. We are, however, 

 certain that in his amended restoration of Acauihodes, Dr. Dean has 

 made the eye very much too small; and there is another unfortunate 

 mistake in his emendation of Fritsch's figure of Plevracanthus, where 

 a large coprolite (specially noted by Fritsch) is made, to do duty for 

 the pelvic cartilage. From an examination of the original specimen, 

 we are also convinced that the so-called " dermal bones of the head 

 roof of Plenracanthus," copied from Davis in fig. 90b, are merely 

 an imaginative reconstruction of an indeterminable fossil, which may 

 or may not be part of an Elasmobranch skeleton. The general 

 results of modern research, however, are admirably summarized in 

 the letterpress, and the general conclusion is arrived at that " of all 

 known stems that of the shark is most nearly ancestral in the line of 

 jaw-bearing vertebrates." 



The chapter on Chimaeroids is naturally brief, and contains no 

 new matter ; but there are two original restorations of the head of 

 Squaloraja and Myriacanthus to show the position of the peculiar 

 rostral spine. The fossil genera referred to the Dipnoi and the 

 doubtfully distinct Arthrodira, are treated more from personal ob- 

 servation. There is a good new restoration of the Devonian Dipnoan 

 Dipterus, another of Plianeropleuron ; a modified restoration of 

 Coccosteus, in which the upper dorsal fin-supports are made to 

 form a slight lobe, while the tail is nearly diphycercal; an entirely 

 new restoration of Diuichthys much on the plan of Coccosteus, and 

 a page of sketches of the mandible of Arthrodira, from the Cleve- 

 land Shale of Ohio. The latter are particularly interesting as 

 showing the remarkably varied modifications of the teeth in these old 

 armoured fishes. Mylostoma, for instance, with loose grinding teeth. 

 is now definitely proved to belong to this group, although most of 

 the genera* have either conical or shear-like teeth. On the whole 

 Dr. Dean is inclined to believe that the Arthrodira differed more 

 widely from the typical Dipnoi than did these from the ancient 

 sharks. They may, he thinks, be ultimately regarded as worthy of 

 rank as a class. 



The Teleostomi seem to be less satisfactorily treated than the 

 previous groups. This is probably due to their great numbers ami 

 innumerable variations. They are subdivided into Crossopterygii 

 and Actinopterygii, and Dr. Dean admits that the former may have 

 been ancestral, not only to the latter, but also to the Dipnoi. 

 A slightly amended restoration of Holoptycliius is given, and there is 

 a copy of Whiteaves' restoration of Eusthenopleron ; but the other 

 two figures illustrating the more primitive Crossopterygians are 

 unfortunateky Pander's restorations of Gyraptychius and Osteolepis, 

 which modern researches have proved to be in many respects 



