BOTHRIOLEPTS. 



107 



No tail has ever been observed in any of the very numerous specimens which 

 have occurred, so that this part, as in Bothriolepis, could not have possessed any 

 elements capable, or at least easily capable, of preservation. We shall presently 

 see that evidence, not only of the existence of a tail in Bothriolepis, but of its actual 

 configuration, has at last been obtained. 



Remarks. — In the form of the carapace, and in the apparent absence of a tail, 

 this little creature reminds us of Bothriolepis, though the contour of the anterior 

 margin of the dorsal part of the carapace is somewhat different, not only from that 

 in that genus,* but in any other Asterolepid form known to me. The articulation 

 of the anterior median dorsal plate is also quite peculiar, so that, in spite of Jaekel's 

 strictures on the use of such a character as generic, I must still maintain that the 

 genus is entitled to stand. 



Geological Position and Localities. — Peach's specimens were derived from certain 

 flaggy beds belonging to the uppermost division of the Orcadian series at John 

 O'Groat's, Caithness, where he found them in 1863 along with two other fishes, 

 then also new to science, namely, Tristichopterus alatns (Egerton) and Dipterus 

 macropterus (Traquair). Since that time up to the present none of these fishes have 

 been obtained from John O'Groats, but eight years ago 1 Dr. J. S. Flett came upon 

 all three in the grey flags of Deerness, in Orkney, in which they are common, and in 

 fact constitute the only identifiable fossils. The Deerness specimens are not so 

 nicely preserved as those from the original locality, but the identification of the 

 John O'Groats horizon in Orkney by means of those fishes is a matter of great 

 geological interest. 



Bothriolepis, Mchwald, 1840. 



Olvptostetts, Agassiz. 

 Pamphracttjs, Agassiz. 

 Placothorax, Agassiz. 

 Homothorax, Agassiz. 

 Odontacanthtjs, Agassiz. 



Bothriolepis, Agassiz (pars). 

 Pterichthys, Agassiz, et cet. auct. (pars). 

 Asterolepis, Pander (pars). 

 Stenacanthus, Leicly. 

 Holonema, Cope (pars). 



Generic Characters. — Premedian plate of head not notched in front; post- 

 median small, not excluding the median occipital from the posterior boundary of the 

 orbit ; extra-lateral, if present, small and narrow. Posterior commissure of the 

 lateral line system on the head, formed by a V-shaped groove, the apex of which is 



1 Flett, J. S., "On the Discovery in Orkney of the John O'Groats Horizon of the Old Bed 

 Sandstone," ' Proc. Roy. Phys. Soc. Edinb.,' vol. xiii, 1896, p. 255. See also the same author's paper 

 on " The Old Red Sandstone of the Orkneys " in ' Trans. Roy. Soc. Edinb.,' vol. xxxix, pt. 2, 

 pp. 383-424. 



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