34 Recieicii — Karjnnshy on Helicopt'lon. 



described under the name of Edestus from Carboniferous strata in 

 Noi'tli America, Russia, and Western Australia ; but no 'specimens 

 at all approaching the two best of the fossils now made known 

 by Dr. Karpinsky have hitherto been discovered. The rival theories 

 by which Edestus has been sometimes ascribed to the jaws, some- 

 times to the external dermal armour of a shark or skate, can thus 

 be discussed again in the light of important new facts. If the 

 Edestidae must still remain as Elasmobrauchs of uncertain zoological 

 position, the memoir before us at least makes great accessions to 

 our knowledge of the essential points in the structure of their 

 so-called segmented spine. 



The new fossils forming the subject of the memoir were discovered 

 by Mr. A. Bessonow in the Permo-Carboniferous (Artinsk Series), 

 near Krasnoufimsk, in the Government of Perm. They comprise 

 two nearly complete spirals from 0'238 m. to 0-260 m. in diameter, 

 besides three fragments, and were sent by their discoverer to the 

 Museum of the Imperial Geological Survey, St. Petersburg. The 

 ends of both spirals are incomplete, but both exhibit approximately 

 3^ whorls, all in one plane and appai'ently bilaterally symmetrical. 

 The segments or teeth of the central whorls are relatively very 

 small, but they rapidly increase in size towards the peripherj^ and 

 are largest at the free outer end. In one specimen 136, in the other 

 specimen 146 segments are preserved or indicated. The segments 

 resemble those of the typical species of Edeshis in all respects, 

 except that the enamel extends far down the middle of the side of 

 the base, and there is a notch at the inner extremity of the base. 

 These two features, together with the remarkable extent of the 

 spiral, are rightly judged by Dr. Karpinsky to be the marks of 

 ix distinct genus, which he names Helicoprion. All the new 

 specimens are placed in a single species, named E. Bessonoici 

 after their discoverer. Edestus Davisi, H. Woodw., from the Car- 

 boniferous of Western Australia, is provisionally referred to the 

 same new genus. 



After a detailed description of the general characters of these 

 remarkable fossils, Dr. Karpinsky illustrates their microscopical 

 structure by a series of beautifully prepared sections. They are 

 shown to consist of vaso-dentine, without any trace of bone-cells ; 

 and the superficial enamel seems to be the ordinary gano-dentine 

 or vitro-dentine. 



Chemical analyses by Mr. B. Karpow are also discussed, and the 

 conclusion is arrived at that the fossil itself consists chiefly of 

 a substance closely resembling apatite. 



Two or three of the specimens exhibit numerous small granules 

 over and around the bases of the segments. These are next 

 treated in great detail, and the description is again illustrated by 

 beautiful microscopical preparations, of which figures are given. 

 Dr. Karpinsky regards these granules as shagreen or placoid scales, 

 though he finally admits that he does not know shagreen granules 

 of precisely the same structure in any other Elasinobranchs. In 

 our opinion they are not dermal structures, but the well-known 



