250 ON THE PERMIAN CHITONlD^E. 



relied when separating the Howseanian plates from those be- 

 longing to C Loftusianus. Owing, however, to my having mis- 

 laid my only specimen which showed this feature, I was not able 

 to represent it when figuring the species in 1857; and it is only 

 now (August, 1859) that I am enabled, by the discovery of a very 

 interesting plate at Humbleton Hill, to figure the processes, and 

 to speak with safety as to their peculiarity. 



In general form, and in the character of its plates, C. Howseanus 

 possesses many features in common with the recent species C. 

 2Woductus and C. sanguineus ; among its Permian congeners it is 

 certainly most nearly related to C. Loftusianus, C. prisons* of 

 the Carboniferous rocks of Belgium seems to belong to the same 

 elongate type ; as also the upper Silurian species C. Grayanus^. 



It has occurred in the shell-limestone of Tunstall Hill, where 

 it is extremely rare, and at Humbleton Hill. 



3. C. (?) coRDATUs, spec. nov. PL XIIL, figs. 24-27. 

 Intermediate |9?a^es in general form cordate, acuminate pos- 

 teriorly; anterior margin slightly indented; median angulation 

 more or less obtuse ; median line arcuate ; lateral areas faintly 

 indicated ; surface finely granulated, and marked by lines of growth 

 which form rather deep sulcations across the lateral areas. 

 Posterior plate thick, angulated medianly, elevated ; apex pro- 

 minent, reflexed, posteriorly situate; laterally, and towards the 

 anterior margin, an angulation traverses the plate from the 

 apex to each margin; slightly indicated raised lines, radiating 

 from the apex, ornament the posterior surface; processes of 

 insertion somewhat complex; the anterior margin, which is 

 rather thick, is deeply excavated on a plane with the external 

 surface of the plate, and forms an outer groove for muscular (?) 

 attachment ; from near the apex internally spring two lamellae, 

 one on each side, which trend towards the extreme points of the 

 anterior margin, and which, with the inner lip of the groove 

 already mentioned, form a second groove or channelled process of 

 attachment ; this second process is produced into longish 



* Descript. des anim. foss. du terr. carb., p. 321, pi. 23, flg. 1. 

 t Bull, de I'Acad. Koy. dc Belg., 2mc scric, tome iii., no. 11. 



