98 ]MK. G. C. CRICK ON THE MUSCULAK ATTACHMENT OE THE 



of each liinb is rather more deeply impressed than the rest. Within this horseshoe- 

 shaped im])ressiou, and occupying- the median line, is a very fine incised line, which 

 extends backward from about 1 mm. posterior to the anterior boundary of the 

 impression for a distance of about 6'5 mm. Doubtless this horseshoe-shaped impression 

 had to do with the muscular attachment of the animal to its shell, for it has been 

 observed in other forms, but the present specimen does not enable us to trace any 

 connection between this impression and the marks of the muscular attachment seen on 

 the inner edge of the whorl. 



SoNNiNiA, Bayle. 



Sonninia sp. — In the British Museum Collection there is an example (No. C. 5188) 

 of Sonninia sp. from the Inferior Oolite of Yeovil, Somerset, in which the impression of 

 the shell-muscles can be seen (PI. 20. fig. 12). The test has been removed from the 

 internal cast of the whole of the body-chamber, and the impression of each shell-muscle 

 is displayed near the base of the chamber. The specimen has the following dimensions : — 

 diameter of shell 91 mm. ; width of umbilicus (from suture to suture) 28 mm. ; ditto 

 (from margin to margin) 37 mm. ; height of outer whorl 36'5 mm. ; greatest thickness 

 (almost close to the umbilical margin) 24 mm., excluding thickness of test. The body- 

 chamber occupies one-half of the last whorl ; at its base the whorl, or more correctly the 

 internal cast of the whorl, is 27 mm. high and 19 mm. thick. The whorl is subquadrate 

 in section, with nearly jjarallel sides and well-defined inner area, the latter at the base 

 of the body-chamber being about 6 mm. wide and sloping towards the umbilicus, making 

 an angle of about 140° with the lateral area. The boundary of the muscular impression 

 is indicated by an incised line which appears on the inner area of the Avhorl at a point 

 10"5 mm. anterior to the last seiDtum; it jDasses outward and. backward, just crossing the 

 subangular umbilical margin, on to the lateral area, being at about 6 mm. distant from 

 the suture of the shell, and ajipears to almost touch the saddle of the last septum that is 

 situated on the subangular umbilical margin. On the area enclosed by this incised line, 

 and concentric with it, there are several very faint lines, similar to those seen in the 

 impression of the shell -muscles in the recent Nautilus. The surface of the cast anterior 

 and also exterior to this incised line bears a number of shallow and iiTegular indentations, 

 which may have had something to do with the muscular attachment, but the incised 

 line just described appears to have been the impression of the anterior and exterior 

 boundary of the shell-muscle. A similar line and similar adjacent indentations are 

 present on the opposite side of the cast, but no indications of the annulus have been 

 observed in this specimen. 



H A R p o c E R A T I D M, Neumayr, emend. Zittel. 



Hecticoceras, Bonarelli. 

 Meclicoceras hcnticnm, Reinecke, sp. — In the British Museum Collection tliere is 

 an example (No. 22309 a) froiii the Brown Jura e, Dettingen, Wiirtemberg, which 

 displays the impression of the muscular attachment on both sides of the body-chamber 



