74 MR. G. C. CKICK ON THE MUSCULAR ATTACHMENT OF THE 



Speeton Clay, and the latter an Oxfordian Ammonite, now referred to the genus 

 Cardioceras. Then it is proposed to descrihe the form and position of the scars and of 

 the annulus (when seen) in various forms of Ammonoids, ranging from the straight (in 

 the adult) from Bacidites, through Uamites, Crioceras, Ancyloceras, IlacroscapMtes^ 

 Scaphites, and Tnrril'des to the group of the Ammonites ; then in Clymenia and the 

 group of the Goniatites. 



The A^ery fragmentary character, and consequently imperfect determination, of some 

 of the specimens must he mentioned; hut, hearing in mind the position of the shell- 

 muscles in the Ammonoid, viz. on the inner portion of the whorl, it will he at once 

 evident that the traces of the muscular attachment are more likely to he found in 

 fragmentary specimens, principally on natural internal casts of the body-chamber. 



Muscular Scars. 



Tlie muscular scars have been best observed in a fragment of Crioceras qnadratnm *, 

 n. sp., which I obtained from the Speeton Clay of Yorkshire (PL 17. figs. 10, 11). It 

 consists merely of the base of the body-chamber, and is about 38 mm. long. The greater 

 part of the test, which was in a very soft, white, friable condition, has been removed by 

 a stiff brush, so as to expose the surface of the internal cast of the body-chamber without 

 scratching it. The section of the whorl is subquadrate, the outer area being somewhat 

 narrower than the inner ; at the last septum the height of the whorl is 29 mm., and 

 its greatest thickness 27 mm. On the inner (dorsal) area of the internal cast, and near 

 the posterior extremity of the body-chamber, there are two oval areas, one on either side 

 of the median line, the major and transverse diameters of etich being 14 mm. and 11 mm. 

 respectively. The longer diameter of each is placed transversely, but not quite at right 

 angles to the median line, the inner end of this diameter being slightly in advance of 

 the outer extremity. The two impressions ai*e nearly in contact, being only about 

 05 mm. apart at the inner or anterior end of their respective longer diameters ; their 

 posterior borders are only slightly in advance of the last septum. Each impression is 

 very slightly roughened, and consequently distinct from the surrounding and somewhat 

 polished siu'face of the cast. An incised line forms its boundary on the inner, antei'ior, 

 md outer sides, being deepest on the anterior side, while its posterior boundary is 

 marked by a faint, somewhat irregular and imperfectly-defined line. No trace of the 

 portion of the annulus surroimding the base of the body-chamber, and connecting the 

 muscular impression on the one side Avith the muscular impression on the other side, 

 can be seen. In the triangular space between the two impressions, and 3 mm. posterior 

 to the point where they are nearest together, there is near each incised line a veiy 

 small, shallow, double pit, each pair of pits being disposed longitudinally ; these doubtless 

 were connected with the muscular attachment of the animal to its shell. 



* This is really a Bean MS. name. Some of the examples of this species in the British Museum Collection bear 

 this name in Bean's handwriting, and I have adopted tlic name, since, so tar as I know, the species has not j'et 

 lieen described. 



