TKOCHOCEEATID^. 
27 
Trochoceras rapax ?, Barrande. 
1867. Troohoceras rapax, Bai’iande, Svst. Sil. de la Bolieme, vol. ii. 
pt. i. p. 124, pi. xxi., pi. xxii. f. 1. 
1867. Trochoceras pingue, Barrande, ibid. p. 112, pi. xvii. ff. 5-9. 
1877. Trochoceras rapax, Barrande, ibid. Supplem. et Serie tardive, 
p. 89, pi. ccccxciii. ft'. 1-3. 
1882. Trochoceras rapiuv, Blake, British Foss. Ceph. pt. i. p. 225, 
pi. XXX. ft'. 2, 2 a. 
!Sp. Char. This species was known to Barrande only by fragments, 
representing the body-chamber and a few septal chambers. The 
asymmetry, though not considerable, is sufficient for recognition. 
The rate of increase in the body-chamber is 1 in 13. The section 
is subquadrate, being a little flattened in front. The septa are dis- 
tant from each other about T the diameter close to the body- 
chamber, their convexity representing nearly ^ of the ventro-dorsal 
diameter. The siphuncle is subcentral, inclining towards the convex 
border ; its elements are cylindrical. The ornaments consist of 
very prominent annulations, 3| lines apart where the shell-diameter 
is 15 lines ; they scarcely, however, mark the cast. They are 
strongly bent backwards, making a deep sinus along the convex 
border, and completely encircle the shell, showing that it must have 
been evolute throughout a considerable portion of its length. A 
network of stria) covers the test, though only the transverse lines 
can be distinguished with the naked eye. 
liemarhs. This species attains considerable dimensions, a large 
fragment figured by Barrande (pi. xxii. f. 1) measuring 300 mm. in 
length and 230 in its greatest breadth. Professor Blake {he. cit. 
p. 226) observes that “ the general structure of this shell, the shape 
of the section, the position of the siphuncle, the character of the 
ribbing, are very much the same as in Trochoceras gigantemn, to 
which the specimens have been hitherto referred. But in the type 
of the latter . . . the whorls are in contact.” I quite agree with 
Professor Blake that there is nothing to distinguish this species from 
T. p)iague, Barrande. 
The specimen in the Collection which I have referred to T. rapax 
is more perfect than any of those figured by Barrande, a considerable 
part of the coiled portion being preserved, the ribbing and the septa 
are well shown, but the finer ornaments are wanting. The shell is 
much compressed, and therefore it appears to he of a less robust 
habit than T. rapax, but there is no other species so near to it. 
Hoi'izon. Wenlock Shale. 
Locality. Dudley, Worcestershire. 
Bepresented in the Collection by a very fine specimen. 
