350 Viscount (I'Archiac and M. de Verneuil's 



gions, the one ventral, the other dorsal. The internal or ventral region presents from twelve to 

 fourteen longitudinal folds or threads, with pretty equal spaces. Transverse folds, arched from 

 back to front, with wider spaces than the threads, pass over these latter and form little tubercles 

 upon them. Dorsal region more ventricose than the preceding, from which it is separated by two 

 lateral keels. On each side of the back may be reckoned seven rounded folds or threads, more pro- 

 minent than those of the ventral region. Transverse folds, setting oflP from the lateral angles, where 

 they join those of the inner part by a very salient tubercular pinching (pincement), turn back, 

 forming a very elongated S, and describe upon the middle of the back a sinus whose concavity is 

 turned forward. The passage of these folds over the longitudinal folds is also marked by a more 

 or less distinct tubercle. The whole shell is covered with fine, close-set, transverse undulated striae, 

 ■which turn abruptly backward, passing over the back. Aperture transverse, ellipsoidal. Siphon 

 unknown, but probably subdorsal. 

 In young specimens (fig. 2 b.) the threads, as well as the transverse folds, are less prominent and 

 rounded, and are destitute of the tubercle at their point of union. 



The C. Eifelensis differs from the C ornatus in its more numerous threads and in the transverse folds 

 of the dorsal region which are more close-set and continuous, instead of being interrupted. It has four- 

 teen almost equal tubercles upon each fold, while in the C ornatus there are only six, united two by two 

 or in pairs. These two shells are in other respects very nearly related, and it may not be impossible to 

 unite them as varieties when we shall have compared a sufficient number of individuals. At the same 

 time it must be remarked that the characters which have determined us to distinguish them are ob- 

 servable in all stages of growth of each shell. These two species are likewise distinct from the Spirula 

 nodosa of Bronn and of the Bonn Museum. 



The C. Eifelensis is apparently allied to the C. tredecimale (Phil. Pal. Foss., PI. XLIV. f. 215.), but the 

 state of the specimen figured by that author does not permit us to establish a perfect identity between 

 the two shells. Moreover, the C. Eifelensis has fourteen longitudinal ribs instead of thirteen, and the 

 latter number being unequal presents a rare circumstance in these symmetrical shells, the middle of the 

 back of which is usually occupied by a more or less marked furrow. Besides, the transverse striae are 

 filiform and very close, instead of being only four between each transverse rib. Finally, the latter are 

 more numerous than in the shells from Devonshire. 

 Eifel ; rare. 



4. Cyrthoceratites depressus {Cyrtocera depressa), Goldf. Bronn, Leth. geog. PI. 1. f. 5. Tab. nost. 

 XXIX. f. I, 1 a. 



Shell in form of a shortened (surbaisse) cone, arched and forming half a volution, ventricose and ob- 

 liquely depressed at its anterior part. Shell very thick upon the sides, thinner upon the back, 

 marked with fine close-set lines of growth, rising over the back where they cross the suture of the 

 septa at an angle which increases in proportion as these latter are nearer to the aperture. Septa 

 nearly flat, in form of a horse-shoe, very rounded toward the summit of the shell, becoming elongated 

 toward the middle part and presenting near the aperture three-fourths of an ellipsis, the last fourth 

 of which is occupied by a ventral truncation. This truncation, which diminishes in width from the 

 aperture to the summit of the shell, offers throughout this extent three slight undulations, of which 

 one is median and two lateral. This disposition of the septa, which seem to radiate from a point 

 taken at the interior of the ventral curve, agrees with the height of the chambers which is four 

 times greater upon the back than upon the ventral part. Siphon subdorsal, occupied by a bundle 

 of radiating or polypiform fibres, owing undoubtedly to a particular disposition of the muscle of 

 attachment. 



The specimen, which we have figured of its natural size, is very like that which is represented, reduced 



