TROCHOCERAS. 83 



shall see, there is a slight asymmetry discernible in some species of that genus. 

 Nevertheless, they agree so nearly with Trochoceras in so many details of shape, 

 siphuncle, and surface-marks, that I much hesitate to separate them for the one 

 single difference of the amount of asymmetry. 



I. Group of Tr. arduense. 



1. Trochoceras Foordianum, n. sp. PI. IX, figs. 9, 9 a. 



Description. — Shell small, slightly asymmetrical, coiled elliptically in about 

 three volutions, which appear contiguous but not inclusive. Surface bearing 

 strong, steep transverse ridges, arching gracefully backwards from the dorsal to 

 the ventral side, meeting in a blunt angle upon the back, and separated by concave 

 surfaces. Traces of numerous fine spiral lineations crossing the transverse 

 markings. 



Size. — The coiled shell is 26 mm. in length, and 20 mm. in width. 



Locality. — Wolborough. A single specimen is in Mr. Vicary's Collection. 



BemarJcs. — This interesting fossil is, unfortunately, in a very bad state of pre- 

 servation, and therefore neither its internal nor its external characters can be 

 properly made out, though its general nature is sufficiently clear. The appearance 

 of strong, sharp, and regular lineations crossing the ridges is just sufficiently 

 distinct to show that they are not accidental marks. The ribs appear to meet 

 in a loop behind, but this may be intensified by the crushing of the shell. 

 The asymmetry is very slight, but is not, I think, wholly due to the effects of 

 fossilization. 



The termination is absent, and on the supposition that the body-whorl might 

 have been more or less perpendicularly produced, Mr. Roberts and I were at first 

 inclined to regard it as possibly belonging to the genus Lituites, but upon 

 showing it to Dr. Kayser and M. Tschernyschew, thesejgentlemen suggested its 

 comparison with Trochoceras arduense (Steininger)^ which comes from the Lower 

 Beds at Nuremberg, which Steininger calls Llandeilo Flags. 



Salter in his examination of Mr. Vicary's Collection appears to have been much 

 struck with the specimen, and he attached a label to it, " Gyrtoceras, new species, 

 quite new." To this genus, however, it certainly does not belong. There is not 

 a close resemblance in general aspect to Lituites or Ophidioceras, and no reason to 

 suppose that it agreed with them in the character of its body- whorl and mouth. 

 On the other hand, both in its asymmetry and in the style of its surface-markings, 

 it agrees very closely with Trochoceras, and in this genus, I believe, it must be 



1 1853, Steininger, ' Geogn. Beschr. Eifel,' p. 41, pi. i, fig. 1. 



