PYGOPTERUS GREENOCKII, ETC. 707 



bones, may be seen a well-marked suprascapular (50). Between it and the 

 hinder edge of the cranial shield may be seen faint traces of what I should con- 

 sider a supratemporal ossicle. The suprascapular is followed by a fiat and 

 elongated scapula (51), which reaches down, at least, to the middle of the hinder 

 edge of the suboperculum. It is in its turn followed by a large coracoid (52), its 

 lower extremity being seen in fig. 2, exposed by the breaking off of some of the 

 branchiostegal plates. This bone, the upper and larger part of which is flattened 

 laterally with a convex posterior margin, forms below, near the origin of the 

 pectoral fin, a prominent angle, being suddenly bent on itself inwards towards the 

 middle line of the throat. Succeeding the lower part of the coracoid in front is a 

 triangular plate (/), with the acutely-pointed apex directed forwards, and folded 

 on itself laterally, so as to present both a lateral and an inferior or jugular surface. 

 This is certainly the equivalent of the plate succeeding the lower end of the cora- 

 coid in Polypterus, and which is also seen in many of the Crosso/terygidce of the 

 Old Red Sandstone. It is, in the specimen from which fig. 2 was taken, partly ex- 

 posed by the breaking away of some of the branchiostegal plates. 



These are, then, all the facts that I have been able to elucidate with any cer- 

 tainty regarding the structure of Pygopterus Greenockii. Before, however, pro- 

 ceeding to any comparison with the recent Ganoids, let us examine a little into 

 the conformation, as far as can be made out, of the head in certain other upper 

 Palaeozoic genera, viz., Amblypterus and Palceoniscus. 



I have not been able to obtain any further description of the bones of the head 

 in Amblypterus and Palceoniscus beyond that of Agassiz in the second volume of 

 the " Poissons Fossiles." The points to which attention is there directed are : — 

 The projection of the snout in front of the mouth by reason of an expansion of 

 the frontal and nasal bones (ethmo'ide) ; the great extent of the gape ; the strength 

 of the jaws, which are furnished with teeth "en brosse;" that the orbit is 

 bounded below by a series of suborbitals ; that the branchiostegal rays form a 

 series of flattened plates between the two halves of the lower jaw. The opercular 

 apparatus is described as being formed of the usual four pieces, of which the 

 operculum is largest. Of the scapular arch three bones are mentioned, viz., the 

 suprascapular, scapular, and coracoid {humerus). The nasal projection is de- 

 scribed as wanting in Amblypterus. 



Not having been myself able to notice any anatomical difference between 

 heads of Amblypterus and Palceoniscus in such species as have come under my 

 notice, and as my knowledge is principally derived from specimens of Amblypterus 

 from the shales of Wardie, I will assume that genus as the type, believing, how- 

 ever, that all statements regarding its general cranial structure hold equally good 

 with regard to Palwoniscus. After having examined a great number of specimens 

 of Amblypterus* from the above-named locality, I have, in figs. 10 and 11, given a 



* Principally A. punctatus (Agassiz). 



