Foord and Crick — On Prolecanites compressus. 13 



Owing to a fracture, a portion of the cast of the body-chamber can 

 be detached from the rest of the specimen. Its anti-peripheral side 

 display's a concave impressed zone, bounded on either side by a 

 rounded ridge, which bears a very shallow longitudinal groove. 

 Where denuded of the test this anti-peripheral area shows 

 " epidermids," which on the concave portion have the form of 

 short, rather coarse, interrupted, transverse, impressed, wavy lines, 

 but at the ridges on either side they become much finer and more 

 pit-like. The condition of the fossil is such that these epidermids 

 cannot be definitely made out on the sides of the body-chamber; 

 but on the periphery, near its subangular margin, their punctate 

 character can be distinctly seen. 



The character of the septa (see Fig. 5) suggested at once a 

 comparison with such forms as " Ammonites ITensloivi," J. Sowerby,^ 

 and " Goniatites vinctum" J. de C Sowerby.^ 



The type of the latter species, from the Upper Devonian of 

 South Petherwin, Cornwall, is in the Woodwardian Museum, 

 Cambridge, but according to Sowerby's figure its suture-line differs 

 from that of Mr. Wright's specimen in having fewer lobes on the 

 lateral area. 



One of the specimens of " Ammonites HenslowV figured by Sowerby 

 is also in the Woodwardian Museiim, Cambridge, and there are 

 some examples of the species in the British Museum (Natural 

 History). A specimen in the Sowerby collection in the latter 

 Museum, although a cast and partly imbedded in matrix, exhibits 

 the convex periphery with a small portion of shell adhering to 

 the periphero-lateral margin, indicating the former presence of a 

 prominent ridge at this part. 



The writers, however, are greatly indebted to Miss C. Birley, 

 of Manchester, for the loan of an interesting series of examples, 

 whereby most of the characters of this species are clearly shown. 

 All these specimens are casts and exhibit no trace whatever of the 

 shell-structure. 



A comparison with these specimens showed that the septa of Mr. 

 Wright's example agree perfectly with those of Sowerby's species 

 (see Fig. 6), and the general characters of the shell also agree. In 

 Sowerby's species the sides of the whorls are flattened, but they 

 have their greatest convexity at about the middle of the lateral area 

 as in Mr. Wright's specimen. The subangular edges of the peri- 

 pheral area are shown only at one part of Sowerby's specimen, 

 but an example of his species in the Sowerby Collection in the 

 British Museum (Nat. Hist.) exhibits this character and they are 

 particularly well shown in two of Miss Birley's specimens. This 

 character appears, however, to be seen usually only in specimens 

 which have a portion of the body-chamber preserved, for, whilst an 

 example of more than 180 mm. in diameter, but consisting only of 



1 Min. Con., vol. iii. p. Ill, pi. 262, April, 1820. Sowerby figures two 

 specimens ; that represented in the upper figure is in the Woodwardian Museum, 

 Cambridge ; the whereabouts of the other specimen is unknown to the present 

 writers, 2 Xrans. Geol. See. [2], vol. v. pi. 54, fig. 18. 



