THE GEOLOGIST. 



Mr. Davies to compare it with the homologous structure in the 

 teeth of the Fachyrhizodus hasalis of Agassiz, which is described by 

 Sir Philip Egerton, E.R.S., in Mr. E. Dixon's 'Geology of Sussex.' The 

 specimen figured in that work was obtained from the Lower Chalk at 

 Steyning. The characters, which are given, are — " apex very brittle, 

 slightly curved inwardly, and solid ; the base is hollow, and extends 

 into the substance of the jaw." It is further stated that in Sir 

 Philip Egerton' s cabinet there is a specimen of this fish, exhibiting 

 an unusually thick and strong humerus, as well as large and circular 

 scales, covered with asperities so minute as to be indistinguishable 

 without the aid of a glass. 



There are many points of distinction, however, between the Pachy- 

 rhizodus hasalis of Agassiz, and Mr. Mackie's specimen. Apart from 

 the absolute size of Mr. Dixon's specimen, which is at least double 

 that of the one before me, I am wholly unable to detect in the 

 former any trace of that curious sculptured channelling which is so 

 prominent in the latter specimen. This comparison failing, Mr. Davies 

 showed me some most interesting specimens, also from the Folke- 

 stone gault, which exhibited equally perfect evidences of this sculp- 

 turing. I would therefore suggest that some temporary or provi- 

 sional name should be given to this form, which differs from the 

 Fachyrhizodus hasalis of Agassiz, both in its stratigraphical habitat 

 and its odontological conformation. 



The genus Pachyrhizodus, of which comparatively so little is known, 

 has been included in the family Sphyroenoida, of the great division of 

 Acanthopterygian (Cycloid) fishes, in close proximity to such singular 

 aberrant forms as Saurodon and Saurocephalus. We hope that the day 

 is not far distant when some practical ichthyologist may be induced to 

 examine the whole series of sauroid fishes, with a view to their ulti- 

 mate division into precisely determined families. 



Pachyrhizodus glyphodus, Blake and Machie. 



Spec. Char. — Teeth with longitudinal rows of deep sculpturing, parallel with the 

 dental axis. 



COPEESPOKDENCE. 



Glytolepis, Dura Den (Keuper Breccia). 



Deae Sir, — In claiming precedence for Mr. Robert Walker as the first 

 to make public the fact that Holoptychius Fleming} belonged to the genus 

 Grlyptolepis, I ought to explain that this only applies to making it known 

 in this country. Professor Pander, in his monograph on the Saurodipte- 

 rini, stated his belief that the scales supposed to belong to Platygnaihus 

 Jamesoni and II. Fleming/ of Agassiz, were in reality the scales of Ghjp- 

 tolepis leptopterus. The Professor's onhy mistake in this being that those 

 scales belonged, not to G. leptopterus, but to a distinct species of Glypto- 

 lepis, which may be called G. Flcmingi. 



It may also be of interest to some of your readers to be informed that 



