R. B. Newton — Chonetes Pratti in W. Australia. 643 



as in those of a recent species. Its locality is unfortunately unknown. The ventral 

 valve is very deep, with a longitudinal depression along its middle; the dorsal valve 

 is almost flat, with a small elevation towards the front ; both valves are covered with 

 minute strise. The interior of the ventral valve [shows the] occlusor and divaricator 

 muscular impressions. The cardinal spines and their tubuliform orifices are here 

 clearly exhibited. The interior of the dorsal valve [shows the] cardinal process, 

 [the] anterior and posterior occlusor muscular impressions, [the] ovarian spaces (?), 

 [and the] reniform impressions. The granular prominences are here beautifully 

 exhibited. 



To these characters might be added : 



(1) That the external surface of both valves, besides being 

 ornamented with very fine radiating stride, possess subimbricating 

 concentric lines of growth ; (2) that the extent of the cardinal 

 line represents the minimum width of the shell ; (3) that the 

 granular asperites on the interiors of the valves are disposed in lines 

 as they reach the margins, and they are elongate and perforate, 

 presenting the appearance of short tubular spines ; (4) that the 

 external surface of the ventral valve exhibits a number of small 

 orifices placed at irregular distances, which might represent the 

 basal attachments of short spines, a character known to exist in 

 Chonetes papilionacea, G. Ilardrensis, etc. ; and that between the 

 striae or ribs there occur numei'ous minute perforations. 



The dimensions of the figured ventral valve [not given by 

 Davidson] are as follows : — 



Maximum breadth =27 mm. 



Minimum breadth (at cardinal margin) =24 ,, 



Maximum length =19 ,, 



Minimum length =17 ,, 



Depth of convexity = 8 ,, 



Two of the valves from Western Australia represent somewhat 

 larger specimens with the following measurements : — 



Ventral Valve. 



Maximum breadth 



Minimum breadth 



Maximum length 



Minimum length 



Depth of convexity 



Dorsal Valve of another Specimen. 



Maximum breadth 



Maximum leugth 



The deep median depression appears to be a somewhat rare 

 character in the true Chonetes although it is exemplified in some 

 species such as the C. mucronata ^ of F. B. Meek and T. Y. Hayden. 

 This American form, however, differs in other respects from C. Pratti 

 in being widest at the cardinal margin, in possessing a greater 

 number of cardinal spines, and in having its ventral valve of a 

 lesser convexity. 



The general collection of Brachiopoda in the British Museum 

 contains a single dorsal valve of C. Pratti, labelled " Eussia " by 

 Professor Morris, in whose collection it formerly was, which so 

 exactly coincides with the other valves here recorded that I am 



^ Description of some new species of Carboniferous Fossils from the Valley of 

 Kansas River, Proc. Acad. Nat. Sci. Philadelphia, 18o8, p. 262 (not figured). 



