Dr. B. Dean — Fishes, Living and Fossil. 137 



Here Dr. Dean definitely places the remarkable Devonian fossil 

 Palaospondyhis Gunni, which " seems undoubtedly a Lamprey." 

 The Ostracodertns are also provisionally associated with these 

 primitive vertebrate animals, and they are arranged in accordance 

 with the British Museum Catalogue. Dr. Dean points out the 

 close resemblance between the labial plates of Pterichthys and the 

 form of the sides of the mouth in the Lamprey. He also makes 

 the interesting announcement that from personal observation he 

 considers the so-called paired fins of Palceaspis (Claypole) are 

 "merely Elasmobranchian (Chimseroid ?) spines, in crushed con- 

 dition, accidentally associated with the head region of the fossil." 

 The figures illustrating this section, however, are less satisfactory 

 than they might have been. The restoration of Pteraspis does 

 not show the strongly convex ventral shield ; and the figures of 

 Pterichthys do not exhibit the correct position of the labial plates 

 or the large proportions of the caudal fin. There is also a mis- 

 apprehension in the statement (p. 69) that the paired appendages 

 of Pterichthys " are now known to be nothing more than the 

 lateral head angles produced and specialized (i.e. jointed for loco- 

 motion)." The appendages in question never have any connection 

 with the head-shield, but are fixed to a thickened part of the 

 body-armour. 



- The sharks, as might be expected, are very fully treated from 

 the palasontological aspect in chapter iv. The most important 

 perhaps of all Palaeozoic sharks, Cladoselache, from the Lower Car- 

 boniferous of Ohio, occupies the foremost place. All the known 

 species of this shark are of relatively small size, varying in length 

 from two to six feet. In general aspect it is much like a modern 

 shark, with a small horizontal keel on each side at the base of the 

 tail. In many ways, on the other hand, it is the most generalized 

 of known sharks:— "Its paired fins are but the remnants of the 

 lateral fold, serving as balancers; the tail, curiously specialized, is 

 widely heterocercal, its hinder web lacking supports in the upper 

 lobe ; the vertebral axis is notochordal ; and the writer now fiuds 

 that an exceedingly simple condition existed in the neural and 

 heemal arches ; they prove to be of moderate size and' thickness, 

 each a tapering rod of cartilage, forked at its base ; each body 

 segment contains a single neural and heemal spine, closely alike 

 in size. Unlike modern sharks, Cladoselache was without claspers : 

 its eggs must have been fertilized after their deposition, as in the 

 majority of fishes other than Elasmobranchs. The gill openings, 

 at least seven (probably nine) in number, appear, as in the restora- 

 tion, to have been shielded anteriorly by a dilated dermal flap. 

 A spiracle was probably present. The jaws were slender, and 

 apparently hyostylic ; the teeth are of the pattern of shagreen 

 denticles, but occur in clusters (' Cludcdus'). The mouth was 

 terminal in its position. The nasal capsule was apparently not 

 connected with the mouth by a dermal flap. The eye was pro- 

 tected by several rings of rectangular plates, clearly shagreen-like 

 in character. The integument was finely studded with minute 



