Description of the Fossils in the older Deposits of the Rhenish Provinces. 349 



Cyrthoceratites lamellosus seem to unite the Cyrthoceratites to the Orthoceratites. These two last-named 

 wenera are furthermore very nearly related, if indeed one of them ought not to be regarded as a sub- 

 genus. The Orthoceratites are straight in the adult state, but when young the greater number are a 

 little curved, and further we find, according to the species, that the place of the siphon varies from the 

 centre to the margin. If, on the other hand, the character of the Cyrthoceratites is to be curved and 

 involute, and to have the siphon dorsal, an uninterrupted series might be formed from the entirely invo- 

 lute Cyrthoceratites of the mountain limestone of Tournay, to those which are nearly straight, and that 

 including the form proper to the Spirula. 



As to the position of the siphon, it is also subject to great variation ; thus, the Cyrthoceratites aigoceros 

 (Miinster Beitrage, &c., 1839, PI. II. f. 1.) has the siphon median. In the C. cincta of the same author 

 (PI. II. f. 4.) it is also median, but in the C. costata (f. 5.) it is subventral. Then our C. lamellosus 

 presents nearly the same degree of curvature as the C. cincta and the C. costata, nevertheless its siphon 

 is neither central nor ventral, but dorsal. The boundary between these two genera is not well- 

 marked, and it does not appear that it ought to be continued, except to facilitate the study and the 

 classification of the numerous species which belong to them. In a methodical classification we think 

 that the Cyrthoceratites, the Phragmoceratites, the Gomphoceratites, the Actinoceratites, the Conocera- 

 tites, the Ormoceratites, the Conotubularice, &c., ought to Ibrm only subdivisions of the great genus 

 Orthoceratites. 



Paffrath ; common. 



2. Cyrthoceratites ornatus, Goldf., Bonn Museum. Tab. nost., XXVIII. f. 5, 5 a, 5 b. Phil. Pal. Foss., 



PI. XLV. f.217. 



Shell involute, spire formed of at least one volution and a half, depressed perpendicularly in the direc- 

 tion of the involution and increasing rapidly in width. Surface of the shell divided into two parts 

 or regions, one ventral, the other dorsal. The ventral or internal region presents nine or ten lon- 

 gitudinal slight folds, sometimes bifid and separated by equal intervals. These folds, which are 

 more apparent near the aperture than toward the summit, are crossed by fine, close-set, unequal, 

 undulated and slightly lamellar striae of growth. The dorsal region is furnished with three longi- 

 tudinal rows of elevated tubercles which are geminated or united together in pairs. The tubercles 

 of the median row are placed a little behind those of the lateral rows, they are also less elevated, a 

 little elongated and arranged in a zigzag direction. In each pair placed on the side, the tubercle 

 which occupies the lateral keel is larger and more prominent than that of the back, to which it is 

 joined by a sort of pinching up of the shell. This last is sometimes divided into two by longitudinal 

 folds similar to those of the ventral region, and of which five or six are counted on each side of the 

 back. It is the passage of these folds over the little transverse ridges which appears to produce 

 the tubercles. This part of the shell is also covered with close-set, lamellar, undulated lines of 

 growth. Septa slightly concave, irregularly elliptical. The difference between the two diameters 

 augments gradually with age. Toward the summit of the shell this difference is as 3 to 4< and almost 

 as 1 to 2 for the last septum. Siphon dorsal, submarginal, and corresponding to the interval between 

 the median tubercles. 



The form of the septa, the position of the siphon, and the striae of growth, approximate this fine species 

 to the preceding ; but it diff'ers much in its stature, in its tubercles, and in the involution of its spiral cone. 



Paffrath, Eifel ; rare. Newton, Devonshire. 



3. Cyrthoceratites Eifelensis, nob.. Tab. nost., XXXI. f. 2, 2 a, 2 b. 



Shell involute, formed of at least one volution and a half, depressed perpendicularly in the direction 

 of its involution and increasing rapidly in width. Surface of the shell divided into two parts or re- 

 VOL. VI. — SECOND SERIES. 2 Z 



