54 FAUNA OF THE CORNBRASH. 



the axes of which never depart very far from the direction of the circumference 

 of the whorl, the edges seldom being supplied with secondary branches, and, so 

 far as known, never with branches of a higher order. Ex. G. discus. 



Clydoniceras discus (Sowerby). Plate VI, fig. 1 ; text-fig. 5. 



1813. Ammonites discus, Sowerby, Miu. Couch., pi. xii. 



1862. — — Oppel, Pal. Mittli., pi. xlvii, fig. 1. 



1863. (?) — — Lycett, Suppl. Great Ool. Mollusca, pi. xli, fig. 8. 



Type. — Has the following numerical characters : Diameter, 92 mm. Ratio of 

 transverse diameter -82 ; of last whorl '60 ; of thickness '26. The umbilicus is 

 closed when the shell is present, infundibular in the cast. Surface uniformly 

 convex, but bevelled off at the edge, making the sides of the peripheral portion 

 slightly concave. The shell is ornamented with very obscure sigmoid risings, 

 bending forwards rapidly at the outside towards the inner margin of the exterior 

 bevel. The portion of the body chamber preserved occupies half a whorl. The 

 septa are of the same character as those in the specimen here figured, but in the 

 type only one or two are seen in their original condition, the rest being worn down 

 and imperfectly formed. From the " stone quarry near the House of Industry, 

 Bedford." In the British Museum, No. 43942. 



Description. — The specimens of this species examined vary from a diameter of 

 44 mm. to one of 168 mm. The smallest (B. M., 33482) has a very sharp 

 periphery, but is thickest at the smaller end of the whorl. The sides of the keel are 

 slightly concave, but there are no furrows. The ribs are sigmoid but very feeble. 

 At a diameter between 50 and 60 mm. the inner part of the whorl rises into radial 

 undulations roughly corresponding with four outer ribs. These undulations con- 

 tinue till a diameter of about 75 mm. is reached, after which it is difficult to find 

 anything to represent them. The shell when preserved becomes smooth and 

 shining, with only the finest lines of growth, crossed here and there with equally 

 fine spiral lines. The umbilicus appears to be as small as possible through the 

 greatest thickness being very near it. The various sutures are given in text-fig. 5, 

 a — d. They begin as an undulating toothed line, which gradually becomes more 

 complex with growth, the inner lobes and saddles always occupying a forward 

 position, the principal lobes running parallel to the spiral, but increasing in 

 number, the outer lobe and saddle becoming more accentuated and less regular 

 in its running, the lobe being provided with several lobules converging more or less 

 radially towards a centre. 



Distribution. — Specimens referred to this species, as here described, have been 

 examined from Sudbrook (7), Barnwell (1), Thrapston (9), Bedford (4), Kidling- 



