102 ME. G. C. CEICK ON THE MUSCULAE ATTACHMENT OF THE 



to about the middle of tlie inner area, and then turning backward again it disappears in 

 the broken surface of the specimen. The anterior line probably indicates the position of 

 the anterior boundary of the shell-miiscle, and the posterior line possibly the posterior 

 l)0undary of the same ; I think the latter cannot indicate the position of a former 

 attachment of the anterior boundary, for it is not parallel to the anterior line. The other 

 side of the specimen is too badly preserved to show the muscular impression. I have 

 not observed any indications of the position of the annulus iu this specimen. 



Perisphikctes, Waagen. 



Ferisphinctea Achilles, d'Orbigny, sp. — The lateral aspect of the muscular impression in 

 this sj)ecies is clearly shown in an example in the British Miiseum Collection (the smaller 

 of the two specimens. No. 37017) from the "White Jura of Randen, near Schalfhausen 

 (PI. 19, fig. 5). The example is a natural internal c;xst, almost completely denuded of 

 the test. Its dimensions are : — diameter of shell 69 mm. ; width of umbilicus 28 mm. ; 

 lieight of outer whorl 24*5 mm. ; greatest thickness (almost close to the umbilicus) 

 16 mm. The whorl is much compressed, and not much indented by the preceding whorl ; 

 the body-chamber, measured along the median line of the periphery, is about 80 mm. 

 long. The incised line marking the boundary of the muscular iuipression is j)lainly 

 visible at the base of the body-chamber. At the inner edge of the whorl it is 5 '5 mm. 

 in advance of the most anterior part of the last septum ; passing backward and out- 

 ward for a short distance, it is then continued backward as an exceedingly faint line as 

 far as the last septum in a direction nearly parallel to the inner edge of the whorl. The 

 width of the im^u'cssion from the suture of the shell is 2'25 mm., of which only about 

 one-half is visible in the lateral aspect of tiic shell. The boundary of the anterior 

 portion of the scar is more deeply incised than the rest. 



The impression on the other side is similar, l)ut not qviite so distinct. 



There is no trace of the annulus. 



AsPIDOCEKATID^, Zittel. 



Peltoceras, Waagen. 



Peltoceras sp. — The impression of both shell-muscles is well seen on an example of 

 Peltoceras sp. that was found in the Ampthill Clay at Ampthill Tunnel, and that formed 

 part of my late father's collection (PL 20. fig. 1). The specimen, a mere fragment of the 

 natural cast of a large shell, consists of the posterior part of the body-chamber ; it is 

 about 150 mm. long. It is quadrangular in transverse section, and at the base of the body- 

 chamber is 73 mm. high, 65 mm. thick (excludiug the ribs), and 72 mm. thick (including 

 the ribs). An antiperipheral, autisiphoual, or dorsal aspect of the fragment disjilays two 

 longitudinally-elongated oval scars, somewhat pointed anteriorly and bounded by a faintly 

 impressed line. The outer boundary of each area terminates ioimediately above the inner 

 branch of the lateral saddle, while the inner boundary passes down close to the outer side 

 of the antij^eripheral (or autisiphoual) saddle on the same side. The anterior extremity 



