Reviews — A. S. WoochcarcVs Catalogue of Fossil Fishes. 125 



fin and spine is quite right, but I am not so certain that making two 

 separate families Ischincanthidie and Diplacanthidoi out of those with 

 two is equally justifiable. The only difference which Mr. Woodward 

 gives between these two supposed families is the absence of " clavi- 

 cular " bones in the former and their presence in the latter, and I, 

 for one, am at present perfectly convinced that the element which 

 he calls "clavicle" in Diplacanthiis is identical with that which he 

 considers as " basal cartilage " in Acnntliodes and Ischuacantlius. It 

 seems also somewhat inconsistent, that he should give in his definition 

 of Diplacavthus "a pair of free spines situated between the pectoral 

 and pelvic fins," while he persists in rejecting the genus Mesacanthtis, 

 which is distinguished from Acanthodes by the possession of that 

 identical character ! 



HOLOCEPHALI. 



Next come the Holocephali with the single order Chimseroidei, 

 which is divided into the four families of Ptyctodontid^, Squalo- 

 raiidfe, Myriacanthidaj, and Chima^ridfe. After these have been 

 treated of we have a section upon the isolated Ichthj^odorulites, 

 some of which aj)pertained, no doubt, to ChimEeroids as well as to 

 Elasmobranchs. 



OSTRACODERMI. 



We now enter a group of problematical organisms, concerning 

 whose position, the analogy of recent forms affords us compara- 

 tivel}?^ little clue ; these are the Cephalaspides of Agassiz, minus the 

 Coccosteans. The Coccosteans and Asterolepids were removed by 

 M'Coy from Agassiz's Cephalaspides to form the order Placodermata, 

 the remainder were divided by Lankester into two well-marked 

 though allied groups, the Heterostraei and Osteostraci, exemplified 

 by Fteraspis and C'ephalaspis respectively. These two groups form 

 the Ostracodermi of Cope, who considered them to be Agnatha, as 

 no remains of lower jaw had been discovered in them ; latterly he 

 hinted that the Asterolepids which he had previously assigned to 

 the Asoidians, as a group termed Antiarcha, might also belong 

 here. This is the grouping now adopted by Mr. Woodward, but 

 he takes the additional step of replacing these creatures among the 

 fishes, justly remarking, " That there were no hard parts around 

 the mouth and in relation to paired appendages capable of being 

 preserved under ordinary conditions of fossilization seems to be 

 satisfactorily demonstrated ; but there is no justification for any 

 further statement that jaws, pectoral and pelvic arches were absent." 

 And certainly it seems difficult for any one to take into consideration 

 the fact that the plates of PtericJithys are made of true bone, to 

 look at its system of lateral sense-canals, as well as its scaly tail 

 and fins, and yet to doubt that it is really a fish. Mr. Woodward's 

 comparison of the structure of the Asterolepids and Ostracostei is of 

 great interest, pointing out, as he does, the similarity of the position 

 of the orbits and of the interorbital pineal plate, the resemblance of 

 the scaly tail of Pterichthys to that of Cephalaspis, while he at 

 the same time finds an analogy between the ventral shields of 



