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SCIENCE 



[N. S. Vol. XXVIII. No. 714 



but a transverse flexure across the middle of 

 that plate proper. But even apart from the 

 question of the shape of the pineal element, the 

 genus Protitanichthys is obviously founded on 

 doubtful grounds. As Dr. Eastman himself 

 points out (pp. 144, 145), it is extremely 

 probable that this cranial shield belongs to a 

 ■true Coccosteus, perhaps to C. occidentalis or 

 "to the so-called Liognathus spatulaiuSj both of 

 ■which are known only from single elements 

 found in the same formation (Delaware lime- 

 stone, Delaware, Ohio). In view of these 

 (Considerations it appears to me that the name 

 Protitanichthys itself is objectionable. The 

 rprefix Pro in generic names ought to be 

 rigidly restricted to such cases only where the 

 ■evidence for ancestral relationship amounts to 

 practical certainty, as, for instance, in the 

 phylogenetic series of the horses or the camels. 



In regard to Acantholepis, also, we are 

 forced to dissent from Dr. Eastman's inter- 

 pretation. Newberry and others have shown 

 that the objects so named are dermal defenses 

 of some indeterminable Arthrodire or Ostra- 

 •cophore. Now Dr. Eastman rejects this in- 

 terpretation and advances the view, upon very 

 filender evidence, that they are " dermal de- 

 fenses of Chimseroids, probably dorsal fin- 

 spines " (p. 78). He speaks of these spines 

 as having exserted and inserted moieties, 

 ■though admitting (p. 79) that the inserted 

 part has never been observed. 



A few minor slips have crept into the text 

 — a circumstance not surprising when one 

 ■considers the mass of detail dealt with. Thus 

 it is stated that no dinichthyid is known to 

 have symphyseal denticles (p. 126), when in 

 1906 the reviewer published two figures of a 

 mandible belonging to the Newberry collec- 

 tion which clearly displays some ten such 

 •denticles.* 



On one or two points we could wish that 

 the figures had been fuller. Eor instance, a 

 description is given of what Dr. Eastman 

 interprets as the parasphenoid of Macropeia- 

 lichthys. When one considers that the struc- 

 ture so named by our author has never been 



* Mem. Amer. Mus. Nat. Eist., IX., 1906, p. 

 118, fig. 11, and p. 149, fig. 25 C. 



adequately described; that among those hav- 

 ing intimate first-hand acquaintance with the 

 specimens some go the length of denying that 

 any structure homologizable with a para- 

 sphenoid at all exists in MacropetalichthySj 

 or indeed in any arthrognath; one wishes that 

 this debatable element had been carefully 

 illustrated, so that whoever wished might 

 judge whether this be a parasphenoid or not. 

 One also could wish that the dentition of that 

 primitive form Dinichthys halmodeus had 

 been figured so that we could have arrived at 

 a clear concept of the peculiarities of these 

 interesting structures. 



And lastly, this review were inadequate 

 indeed, did we not touch upon Dr. Eastman's 

 views on the relationships of the Arthrodira 

 — a group upon which he has bestowed con- 

 siderable time and effort during the past few 

 years and which occupies no less than a 

 quarter (68 pages) of the present memoir. 

 Indeed, his view of the affinity of the Arthro- 

 dira is the veritable Leitmotif which runs 

 through his entire discussion of the group. 



This theory may be briefly stated as fol- 

 lows : a Paleozoic dipnoan gave off two lateral 

 branches of lung fishes. One of these flour- 

 ished through several geological periods, giving 

 rise to Dipterus, Ctenodus, Uronemus and the 

 like, finally becoming extinct; the second 

 branch, constituted the stock of the Arthro- 

 dires, evolved a galaxy of forms, only to be- 

 come extinguished at the close of the Devonic. 

 The central stock of primitive ceratodonts, on 

 the other hand, continued essentially unmodi- 

 fied through all later geological periods and 

 is represented at the present day by the exist- 

 ing lung-fishes. 



Hence Dr. Eastman upholds two distinct 

 theses: (1) that a ceratodont, not a dipterine, 

 exemplifies most nearly the primitive dipnoan ; 

 and, (2) that the Arthrodira are specialized 

 offshoots of this primitive ceratodont. 



The first of these theses, although contra- 

 vening the widely accepted view elaborated 

 by Dollo and others, our author does not treat 

 at any length in this memoir and we need not, 

 therefore, go into it.° As for the second, the 



' For a critique of Pr. Eastman's views on this 



