CLYDONICERAS LEGAYI. 57 



then we can verify the statement of Neumayr that it is found in England, 

 though he gives no details except mentioning that it is from the zone of 

 Macrocephalus. A specimen showing the peculiarities relied upon is in the 

 British Museum (33541) said to have been obtained from the Cornbrash of 

 Trowbridge (PL VI, fig. 3). This has a diameter of 80 mm. The half of 

 which it is composed seems to consist entirely of body-chamber. The ribs 

 are fairly straight at first but towards the periphery they bend rapidly forwards ; 

 later they become rougher and more separate and then soon die away. This 

 would appear to indicate an adult form. The breadth of the periphery also 

 diminishes and the shell becomes almost of the shape of C. discus. The siphuncle 

 is seen in the cross-section to lie below the level of the keel. So far there is 

 nothing distinctive, but two other features are only seen in the specimen and 

 description given by Brauns. The transverse section exposed by fracture shows 

 by the matrix which fills the umbilical cavity that that cavity was larger at 

 one time than at a later, the diameter of the cavity decreasing with growth from 

 C-5 mm. to 5 mm. The sutures also are of the character observable in Brauns' 

 figure ; that is to say, they recede farther from the aperture to a point consisting 

 of a central prong and two minor side ones. There is, however, only one specimen 

 which shows those features. It is even accompanied by a smaller specimen which 

 has a furrow on either side its keel and shows no sutures. 



Further information is very likely to throw light on the relations of this 

 species to the other Clydonicerata . If it had not been for Neumayr's giving 

 it a name, it would probably have been included in C. legayi, though it is difficult 

 to imagine how a suture with a central lobe of two teeth could possibly change 

 into one with triple teeth. 



Distribution. — A single specimen from Trowbridge. 



Clydoniceras legayi (Rigaux and Sauvage). Plate VI, figs. 4, 5, 6. 



1867. Ammonites legayi, Kigaux et Sauvage, Mem. Soc. Acad. Boulogne, vol. iii, p. 21, pi. i, figs. 1, 2. 



Type. — " Discoid, very compressed, keeled, with broad, nearly flat whorls, 

 ornamented with flexuous ribs ; back square, with a small keel bounded by two 

 narrow furrows. Umbilicus small. The external borders are angular." The 

 specimen is only 30 mm. in diameter, and is from the " Calcaire des Pichottes," 

 recognised later as Cornbrash. 



Descrijitioii. — The most nearly perfect specimen seen (PI. VI, fig. 4) has a 

 diameter of 35 mm., to which its transverse diameter has a ratio of *82 and last 

 whorl -57. The thickness cannot here be measured. The umbilical edge is very 

 clearly marked, almost swollen, and the inside nearly vertical ; the triangular 



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