560 RAMSAY H. TRAQTJAIR ON AMBLYPTERTJS, 



/. ovatus of "W. C. Redfield, species originally referred by that 

 author also to Palceoniscus, though he was not unaware of their 

 essential differences from that genus, and of the likelihood of their 

 being eventually separated. For in alluding to the stout character 

 of the fins and their insertions, whence the specific name fultus, 

 given by Agassiz, he says that " this character is also found to 

 pertain in a greater or less degree to all the American species of the 

 genus, and would perhaps warrant their separation from the 

 Palceonisci " *. He notices, further, the great strength of the 

 fulcra, their comparatively small number, and unequal length and 

 inclination, and, as regards the tail, that the scales of the body are 

 prolonged into the upper lobe, " but to a more limited extent than 

 in the European species of the genus." The small extent of the 

 gape has also been mentioned by Sir Philip Grey-Egerton. 



Ischypterus was classed by Sir Philip Grey-Egerton among the 

 Ganoidei Heterocerci (= Lepidoidei Heterocerci, Ag.) along with 

 Palceoniscus and Amblypterus ; more recently, however, it has been, 

 by Prof. J. Y. Carus, disassociated from the Palaeoniscidoe and 

 placed among the Sauroidei as remodelled by Dr. Andreas Wagner. 

 But as I have hitherto seen no detailed account of its structure, I 

 may here give a few particulars concerning /. latus, which will 

 clearly show how widely this genus deviates, not only from 

 Palceoniscus, but from the entire group of Paheoniscidae. 



In Ischypterus the body is rather deep, and strongly arcuated in 

 front of the dorsal fin ; the scales are rhomboidal and smooth ; but 

 along the middle line of the back, from the occiput to the dorsal fin, 

 there extends a row of peculiarly shaped median scales, like those in 

 Semionotus Bergeri, Ag., and Lejndotus minor, Ag., these being 

 somewhat spur- shaped, with posteriorly directed points, and 

 imbricating over each other from before backwards. They were 

 pointed out by Mr. W. C. Kedfield, who says of them that they were 

 " sometimes mistaken for an anterior comblike dorsal." The caudal 

 fin is comparatively short and small ; it is hardly cleft, being only 

 somewhat concave behind, and is, moreover, nearly symmetrical in 

 external form, the upper projecting point only passing a little 

 further back than the lower. The prolongation of the body-scales 

 along the upper margin of the fin is very narrow and rapidly 

 attenuating, and, although it reaches nearly to the extremity of 

 what may be called the upper lobe, is very short, owing to the 

 shortness of the fin itself. The rays are comparatively few in 

 number, those of the upper lobe gradually diminishing in length 

 towards its extremity ; and the fulcra, which run along the margin 

 of the lower lobe, are nearly as strong as the V scales, usually also 

 called fulcra, which border the upper one above. Though this form 

 of tail cannot be called " homocercal," inasmuch as a scaled pro- 

 longation of the body does extend nearly to the point of the upper 

 lobe, yet, from the shortness, feebleness, and attenuation of this 

 prolongation, along with the striking reduction of the number of 



* Am. J. So. xli. 184], p. 25. 



