128 FOSSIL FISHES OF THE ENGLISH CHALK. 



Zone of Holaster subglobosus : Ditch ling, Sussex ; Burham, Hailing, Cuxton, and 

 Folkestone, Kent. Turonian zones : neighbourhood of Lewes. Zone of Micraster 

 coranguirmm : South Croydon, Surrey. 



3. Pachyrhizodus dibleyi, A. S. Woodward. Plate XXVI, figs. 1—4. 



1901. Pachyrhizodus dibleyi, A. S. Woodward, Catal. Foss. Fishes B. M„ pt. iv, p. 38, text-fig. 3. 



Type. — Premaxilla and portions of maxillae from zone of Holaster subglobosus ; 

 British Museum. 



Specific Characters. — A robust species, attaining a larger size than P. gardneri. 

 All teeth with a remarkably stout and much -expanded base, and a comparatively 

 short stout crown, which is scarcely, if at all, incurved at the apex. Premaxilla 

 about twice as long as broad. Maxillary teeth in very irregular series, the bases 

 of those in the hinder portion excessively compressed antero-posteriorly. 



Description of Specimens. — The type specimen is an associated set of remains 

 of the upper jaw, exhibiting the characteristic teeth, though very much broken. 

 The premaxilla (PI. XXVI, figs. 1, 1 a) must evidently have been comparatively 

 long and narrow. One of its posterior marginal teeth (m.) is about as large as an 

 anterior maxillary tooth ; while the posterior inner tooth (/.) well displays the 

 relatively wide base and the blunt stumpy crown, which is a little worn at the apex. 

 The anterior inner tooth is represented only by its socket. The maxilla (figs. 2, 3) is 

 very stout and of coarsely fibrous texture, with a large antero-internal process (p.) 

 for union with the premaxilla. The right and left maxillae are similar in shape 

 and size, so far as they can be compared, but the teeth of the two sides are very 

 different and quite irregular in disposition. All the teeth preserved are worn and 

 blunt at the apex; and the antero-posterior compression of their base is especially 

 well seen in the displaced tooth shown in fig. 2 a. A laminar bone of the pterygoid 

 arcade is covered with a dense cluster of minute conical teeth. 



The tooth-bearing ledge of a dentary bone discovered separately by Mr. Dibley 

 (PI. XXVI, fig. 4), evidently belongs to this species, exhibiting teeth of the 

 characteristic shape, which are very slightly curved at the apex. The articular 

 end of the same mandible has a coarsely fibrous structure. 



Horizon and Localities.— Zone of Holaster subglobosus : Burham, Kent ; 

 Merstham, Surrey. 



