Reviews — Br. 0. Jaekel — Armoured Palceozoic Sharks. 423 



tudinal series of spinous tubercles. Of the cartilages of the head 

 and trunk nothing is visible ; and in the paired fins there are only- 

 feeble traces of nearly parallel rays. No median fins can be seen ; 

 and the dentition is doubtfully inferred from fragments to have 

 consisted of Cochliodont plates. 



Dr. Jaekel was led to the investigation of Menaspis by his studies 

 of Ichthyodorulites, detailed in the first and third of the memoirs 

 quoted above. The result is most gratifying to those who recognize 

 in this fossil, as now elucidated, the dawn of our knowledge of the 

 Paleeozoic armoured Sharks. At the same time, however, it is much 

 to be regretted that before launching into broad speculations, the 

 author did not further take advantage of the kind offices of Prof. 

 K. von Fritsch, and borrow for study another of Giebel's Kupfer- 

 schiefer fishes — Dichelodus acutiis. If this be correctly interpreted 

 in the original memoir (Zeitschr. gesaramt. Naturw. Halle, 1857, 

 p. 121, pi. iv.), it affects very materially some of Dr. Jaekel's gene- 

 ralizations concerning " Trachj'^acanthidfe "; and we venture to think 

 that an examination of it would have considerably modified many- 

 matters which we regard as baseless imagination. 



Whether, indeed, from an imperfect acquaintance with English, or 

 from defective memory, or hasty work, Dr. Jaekel's theoretical 

 remarks are full of misconceptions, which it may be of advantage in 

 some respects to point out. In the fii'st place, he arranges dorsal 

 fin-spines in three divisions — the " Cestraciont," the " Acrodont," 

 and the " ChimEsroid " — according to the form of their transverse 

 section. We would remark that Nemacanthus (termed " Cestraciont ") 

 and Ctenacanthus (termed "Acrodont") have in fact the transverse 

 section and lateral denticles described by Dr. Jaekel as exclusively 

 " ChiraEeroid " ; whereas the dorsal fin-spines of the Myriacanthidae, 

 which are certainly Chimgeroid, present differences again. In the 

 first memoir, too, a whole page is devoted to a fundamental miscon- 

 ception of Gyracantlius ; but this is cancelled (as the result of an 

 interview with Dr. Ti-aquair) by a footnote in the second memoir. 

 Finally, Dr. Jaekel places all the paired Ichthyodorulites, e.g., 

 Oracanthus, Erismacanthus, Physonemus, Gamps acanthus, etc., in a 

 new " group " termed " Trachyacanthidse " and in the original 

 memoir this is regarded as including both the Cochliodontidge 

 and the Chim^roid genera, Myriacanihus (" Prognathodus ") and 

 CMmceropsis. 



The latest researches on the Myriacanthidse, however, of which 

 Dr. Jaekel overlooked the preliminary results in his first contribution, 

 have caused a considerable modification of the " group Trachyacan- 

 thidee " in his second memoir. Menaspis is still retained as a member 

 of the new group, and made, in fact, its type ; but the Myriacanthidse 

 are now declared to be " entirely different." So far all will doubtless 

 be in accord with Dr. Jaekel ; but when he raises this group to rank 

 as a distinct division equivalent to — and intermediate between — • 

 the " Selachier " and " Chimaeriden," few will be satisfied with the 

 available evidence. 



Here, again, several fundamental statements require correction 



