﻿BRITISH FOSSIL CEPHALOPODA. 221 



Trochoceras regulare, Blake, PL XXIX. fig. 7. 



Type. — The rate of increase is 1.5, and the last whorl is .33 of the whole. The 

 section is a rather flattened oblong, rounded at the edges. The whorls slightly 

 overlap, and there is decided asymmetry. The ornaments consist of very clean and 

 separate backward-curving ribs 22 per whorl, which stand out from the flat surface 

 in the centre of the whorl, but die away partially over the front. The whole is so 

 covered with the shell, that no septal characters are observable, and it is unknown 

 how much belongs to the body-chamber. From the Wenlock Limestone, Dudley. 

 In the British Museum. 



General Description and Relations. — No other example of this very distinct form 

 has been seen. In shape it is nearest to Nautilus quadrans, but its ornaments are 

 different. 



Distribution. — In the Wenlock Limestone, Dudley (1). 



Trochoceras tortuosum, Sowerby, PI. XXXI. figs. 3, 3a. 



1839. Lituites tortuosus, Sowerby in Murchison's ' Sil. Syst.' pi. 11, figs. 3, p. 622. 

 Syn. 1865. Trochoceras oxynotum, Barrande, ' Syst. Sil. de Bolieme,' vol. ii. pi. 14, fig. 1-11, p. 91. 



Type. — Rate of increase 1.29 ; last whorl .3 of the whole. The outer whorls 

 slightly overlap the inner, and scarcely any elevation is observable. The section is 

 rounded-lanceolate, rising to the greatest thickness at -^ the whorl-breadth from the 

 umbilical edge, whence there is a gentle slope to the front, which is subangular. 

 Ratio of thickness to breadth as 13 to 18. No ornaments. The shell is of consider- 

 able thickness. The septa bend slightly backwards on the inner side of the whorl, 

 and then rapidly forwards, meeting at an angle on the front. They are very 

 numerous, 50 per whorl ; the septal surface has a convexity of J- the long diameter 

 of the whorl, the inner part being flatter. The siphuncle is external, in the angle 

 at the front, and has a diameter on the septal surface of -^ the whorl-diameter. 

 Diameter about 30 lines. 



The specimen on which Sowerby's species was founded, which is in the collection 

 of the Geological Society, consists of two pieces, of which the larger only was 

 figured, or perhaps even seen. When put together, they form an ordinary involute 

 Trochoceras. The matrix is a black calcareous nodule, said to be from the Lower 

 Ludlow, between Welchpool and Berriw. 



General Description. — I have only seen one other example which could be 

 referred to this species. It is in the Gray Collection in the British Museum. It has 

 the same shape of section ; the thickness being \\ of the whorl-breadth. The 

 increase is very slight in the body-chamber, here seen, and the curvature con- 



