100 OLD RED SANDSTONE FISHES. 



of the oculars. Pig. 4 on the same plate is an anterior median dorsal plate 

 from Cromarty ; the angles are lost, but the external sculpture of closely set 

 tubercles is clearly given. Fig. 5 is, in like manner, a specimen of the right 

 posterior ventro-lateral plate, also from Cromarty, and nearly entire. Part of the 

 osseous matter is gone, but part also remains, and this sIioavs the same tubercular 

 ornament as in Fig. 4. Lastly, in PL XIX, Fig. 4, we have a detached right posterior 

 dorso-lateral plate from Achanarras, seen from the internal aspect. Here it may 

 be noted that, as the plate has been crushed quite flat, a longitudinal fracture has 

 taken place for three fourths of its extent along the course of the lateral line 

 groove (see p. 93). 



Remarks. — As already indicated, all the reputed species of Pterichthys described 

 by Agassiz and Sir P. Egerton from the Scottish Orcadian rocks, with the 

 exception of Pt. productus (and that may possibly be only a sexual form of the 

 same creature), must find their place under Pt. Milleri, which, although not 

 occurring first in Agassiz' great work on the fishes of the Old Red Sandstone, 

 has priority secured to it by the description and figures previously published by 

 Hugh Miller in his ' Old Red Sandstone.' 



The synonymy may be dealt with as follows : 



Pt. latus (Agassiz). — This is evidently the adult form of the comparatively small 

 specimens figured as Milleri in the ' Poiss Foss. v. gres rouge,' PI. I, Figs. 1, 2, 

 and 3. Types of latus in British Museum and in the Gordon Cumming Collection 

 at Forres. 



Pt. testudinarius (Agassiz). — Founded on the apparently small size of the median 

 ventral plate, of which in the unique type specimen from Cromarty (Agassiz, op. cit., 

 PI. IV, Figs. 1, 2, and 3, and present work, PI. XIX, Figs. 2 and 3) only the 

 sculptured surface is exhibited. The proportions of the ventro-lateral plates agree 

 with those in the majority of specimens of Pt. Milleri. 



Pt. cancriformis (Agassiz). — Agassiz states that the form of the body and head 

 recalls Pt. productus, but that the only difference consists " dans la structure des 

 nageoires pectorales, qui au lieu d'etre coupees obliquement se termine en une pointe 

 longue fine et tres-aceree." An examination of the type specimens, from Orkney, 

 in the British Museum shows clearly enough that the original of Fig. 5, PI. I 

 (Agassiz, op. cit.) belongs to Pt. Milleri, while that of fig. 4 is just as clearly 

 referable to Pt. product/as. 



Pt. cornutus (Agassiz). — Supposed to be distinguished by the presence of a 

 prominent spine on each of the caudal scales, but this is not verifiable on the type 

 specimens, which are all in the British Museum. These type specimens, three in 

 number, are represented on PL II of Agassiz' work on the fishes of the "Old Red." 

 The specimen represented with its counterpart in Fig. 1 of that plate wants the 

 perioral appendages, and sIioavs otherAvise nothing to distinguish it from ordinary 



