RHYNCHONELLA. 97 



discussion of all the synonyms attributed to this form by Professor Bronn, and other 

 authors, as so much uncertainty exists as to the types intended. Both Baron Von Buch 

 and Professor Bronn seem disposed to admit Anomia triloba lacunosa, of Fabio Colonna, 1 

 to be the type of the species in dispute; I am not, however, able to decide the question : 

 but I cannot admit, as stated by the celebrated author of the ' Uber Ter.,' that R. lacunosa 

 is common to the Upper Jura and to the Magnesian or Permian Limestone of Humbleton, 

 in Yorkshire ; the last does not even belong to the same genus, and is the Camerophoria 

 multiplicata, so ably described and figured by Professor King in his valuable ' Monograph 

 of British Permian Fossils.' 



The shell under consideration has been attributed to R. telraedra, var. media? a 

 species I do not know with certainty to occur higher up than the Lias ; the convexity of 

 the valves and form of the beaks in this last easily distinguish it from the shell under 

 notice. 



Figs. 13, 14. From specimens in the collection of Mr. Robertson. 



90. Rhynchonella Hopkinsi, M'Coy, MS. 1852. 



Diagnosis. Shell inequivalve, subcuboidal, valves gibbous, generally longer than wide, 

 sides tumid, nearly vertical, beak acute, incurved, under the extremity of which is seen a 

 small foramen entirely surrounded by the deltidium, beak ridges well defined, leaving a 

 large slightly concave false area between them and the hinge line, which indents the 

 imperforated valve, giving to this portion of the shell a pinched aspect, smaller valve very 

 gibbous, ornamented by a variable number of small acute plaits, from twenty-four to thirty 

 in number, three, four, five, or six, forming a well-defined elevated mesial fold. In the dental 

 valve a very shallow sinus is visible, becoming convex as it approaches and meets the mesial 

 fold ; a number of small lines of growth cover the surface ; structure imperforated, dimen- 

 sions variable. Length 10^, width 9^, depth 9 lines. 



Obs. This elegant shell was noticed for the first time by Mr. Bouchard, who found it in 

 the Great Oolite of Marquise, near Boulogne-sur-Mer, where it is common ; but it was only 

 on a late visit to the Cambridge Museum that I became acquainted with its existence as a 

 British species from the Great Oolite of Minchinhampton, and named in that collection by 

 Professor M'Coy. This species is easily distinguished from R. tetraedra, to which it 

 bears some resemblance, by its square shape and more circular beak. 3 



1 De Purpura Romse, 1616. 



2 Sir R.. Murchison, ' Trans. Geol. Soc.,' vol. ii. 



8 I regret that from all my plates being printed before I became acquainted with the existence of this 

 species in England, it could not be illustrated ; in the Appendix, at the conclusion of this work, it is my 

 intention to figure those new species which may be discovered during tbe interval. 



