PACHYTHRISSOPS. 133 



The anal fin is as deep as the dorsal and closely similar, but more extended, 

 probably with not less than 23 rays. The long foremost support is rod-shaped, 

 and the wings at the articular ends of the other supports are short. The forked 

 caudal fin is well shown in the type specimen, with the step-shaped articulations 

 of its thicker rays. All the hasmal spines within the base of the caudal fin are 

 stout, and two bearing the middle rays arc 1 slightly expanded. There are no 

 traces of fulcra on any of the fins. 



Remains of rather large cycloidal scales are seen in the original of PI. XXIV, 

 fig. 5, but they must have been very thin, and are usually absent in the fossils. 



Remarks. — When examples of Pachyihrissops Isevis were first described, they 

 were provisionally ascribed to the Wealden species treated below ; but the form is 

 readily distinguished by the characters of the opercular apparatus and the sharp- 

 ness of the lateral ridge on the caudal vertebras, besides by the proportions of 

 the head. 



Horizon and Locality. — Middle i'urbeck Beds : Swanage, Dorset. 



2. Pachythrissops vectensis, A. S. Woodward. Plate XXIV. figs. 6, 7; Plate 

 XXV, figs. 4, 5; Text-figure 40. 



1890. Oligopleurus vectentix, A. S. Woodward, Proc. Zool. Soc, ]>. 34fi, pi. xxviii, fig. 1. 



1911. Oligopleurus vectensis, E. H. Traquair, Poiss. Wealdiens de Bernissart, (Mem. Mus. Roy. Hist. 



Nat. Belg\, vol. v), p. 47, pi. x. 

 1913. Oligopleurus vectensis, E. S. Goodrich, Proc. Zool. Soc, p. 84. 



Type. — Head; British Museum. 



Specific Characters. — Attaining a length of a little more than a metre. Length 

 of head with opercular apparatus about equal to the distance between the paired 

 fins. Operculum apparently without slime-pit, smooth, or faintly rugose, but 

 fimbriated at the postero-superior border; preoperculum with a few strong 

 radiating ridges spaced over the lower limb. Vertebras 35 in abdominal region ; 

 centra in caudal region not longer than those in abdominal region, without any 

 sharp lateral ridge, but slightly indented above and below to produce a broad 

 rounded lateral ridge. [Fins imperfectly known. J Scales ornamented with sparse 

 pustulations, and more or less fimbriated at the hinder border. 



Description of Specimens. — The type specimen is an imperfectly preserved skull 

 and mandible shown of one-half nat. size from the right side in Text-fig. 40. The 

 greater part of a fish (PI. XXV, fig. 4) discovered by Mr. Reginald W. Hooley, 

 F.G.S., exhibits the head and most of the vertebral axis, besides some remains 

 of fins. Other more fragmentary specimens make known a few additional details. 



The skull is always more or less crushed and broken, but many of its principal 

 features are shown in the fossils. As seen in the type specimen, there is a well- 



