﻿166 BEITISH FOSSIL CEPHALOPODA. 



interior only is seen, and this shows a lateral siphuncle of f- the whole diameter. 

 The septa are now oblique, probably by contortion, and are distant -|- the diameter. 

 On reaching the siphuncle, they bend slightly upwards towards the aperture ; 

 though the chambers here stop short, the septa are continued over the siphuncle 

 slightly bending upwards, and along the latter is a depressed line. Thickenings of 

 the shell in the chambers have left depressions between the septa sloping up at 

 a greater angle than themselves. Length, 10 lines; diameter, 5 lines. From the 

 Arenig Beds of Lord's Hill, Shelve. In the Museum of Practical Geology. 



Relations. — This cannot be an Endoceras, as the septa certainly do not make 

 sheaths pointing backwards, nor have we any proof that it is a Tretoceras. Hence, 

 though the inclination forward of the septa is not nearly- so marked as in 

 Barrande's examples, it belongs, I think, to the above subgenus, and its special 

 character is this very feebleness of forward inclination of the sutures. 



Distribution. — Only the type is known. From the Arenig, Shelve. 



Genus Cyrtoceras. 



Section Endogastrica. 

 Cyrtoceras precox, Salter, PL XYIII. figs. 6, 7. 



1866. Cyrtoceras precox, Salter, ' Mem. G-eol. Surv.' vol. iii. pi. 10, fig. 3. 



Type. — This is a short fragment imbedded in the slate (fig. 7), in such a way 

 that only one end of it is seen — the rest being still covered — so that the outline at 

 the base is not that of the shell. On the apparently concave side a fragment is torn 

 up at right angles, which being replaced would remove the appearance of concavity. 

 For these reasons I was inclined to regard this specimen as merely a contorted 

 0. sericeum. Nevertheless the septal lines have somewhat of the curvature of a 

 Cyrtoceras, and part of the exterior boundary looks convex. Hence, another 

 undoubted Cyrtoceras of similar age having been found, this may be admitted. The 

 septa curve backwards towards the convex side, and are distant ^ the diameter. 

 The body-chamber is shorter than its basal diameter, and the aperture has a 

 forwardly curved outline. The greatest diameter is nearly ^ inch, and the length 

 preserved nearly 1 inch. From the Lower Tremadoc Slates, Llanerch. In the 

 Museum of the University College for Wales, Aberystwith. 



General Description. — Another example (fig. 6) is a more satisfactory Cyrtoceras. 

 No section is seen ; the curvature has a mean radius of 3^ inches. The rate of 

 increase is about 1 in 4. Across the surface are a number of parallel folds ; but 

 whether they are folds of growth, and the deeper lines the septa, or whether they 



