Description of the Fossils in the older Deposits of the Rhenish Provinces. 351 



to a third, in the Lethcea geognostica (loc. cit. supra) ; but, besides this latter figure not giving any idea of the 

 remarkable disposition of the septa, it is otherwise inexact in the height of the chambers on the ventral part, 

 not having been diminished proportionally to the rest of the shell, appearing double their proper height. 



Var. a. Shell distinguished from the preceding by a distinct, central, dorsal keel, which gives a penta- 

 gonal form to the septa. 



We must observe, that it is to the unequal increase of the opposite edges of the chambers that the 

 shells of this group owe the obliquity of their septa, and consequently their curved form, which, as may 

 easily be conceived, is so much the stronger as the inequality is greater. Completely involute shells, 

 like the Goniatites, show this difference at its maximum. Nevertheless, in the Cyrthoceratites depressus 

 this curvature is relatively slight ; but this arises from the circumstance, that to the preceding differences 

 in the height of the same chamber, there is added a much more distinct compression toward the aper- 

 ture than toward the summit, and at the same time a rapid increase in the diameter of the shell. 



Eifel ; rare. 



5. Cyrthoceratites Uneatus, Goldf., Bonn Museum. Tab. nost., XXX. f. 2, 2 a. 



Shell conoidal, short, very slightly arched, very thick, marked externally with irregular, simple, sinuous 

 lines of growth, which turn backward and pass above the siphon. The internal lamina of this shell 

 presents longitudinal folds on each side of the back, which are often obsolete, but still distinct 

 enough. A broad shallow depression is to be observed in the middle of the concave part opposite 

 to the siphon. Septa nearly flat, suborbicular and horizontal toward the summit, ellipsoidal and 

 oblique as they approach the aperture. Upon the back the chambers are twice and a half the height 

 they are on the ventral side. Siphon round, nine millimetres in diameter, and placed ten milli- 

 metres from the dorsal or convex margin of the shell. 



Paffrath, Eifel ; rare, 



6. Cyrthoceratites tetragonus, nob. Spirula dorsata, Bonn Museum. Tab. nost., XXXI. f. 3, 3 a. 

 Shell quadrangular, slightly arched, presenting longitudinal tubercular folds, with equal interspaces, 



upon the two outer angles. Inner angles simple. Septa numerous, near together, with undulated 

 edges, concave on each surface and rising toward the aperture at their passage over the angles. 

 Siphon small, subdorsal. Shell smooth or only marked with striae of growth. 

 Eifel; rare. 



Phragmoceratites subventricosus, nob. Cyrthoceratites compressus, Goldf., Bonn Museum, Tab. nost., 



XXX. f. 1, 1 a. 

 Shell in the form of a slightly elevated cone, compressed upon the sides and slightly arched, so as to 

 present only half a volution when the shell is complete. Septa slightly concave, elliptical, having 

 their greater diameter between the back and the ventral part, and being also a little sinuous anteriorly 

 on the dorsal region. Chambers two and three times higher dorsally than ventrally. Siphon ventral, 

 very near the edge, and madreporiform. 

 This shell differs from the preceding in the position of the siphon, which is ventral, or placed on the 

 concave face, and in its compression, which is parallel to its curve, instead of being perpendicular to it. 

 These two characters, if constant, would justify the subdivision established under the name oi Phragmo- 

 ceratites. Our species, however, is distinguished from Phr. ventricosus (Broderip, Sil. Syst., PI. X. f. 4 — 6) 

 in being less compressed, which renders its two diameters less unequal. This difference accords with that 

 of its geological position ; Mr. Murchison's species being found in Norway, as in England, in the Silurian 

 System, while ours belongs to the Devonian System. 

 Eifel, Refrath ; rare. 



1. Conularia Gervillei, nob. Tab. nost., XXIX. f. 3 and 4, -t a, 4 i, 4 c. 



Shell straight, forming a very compressed quadrangular pyramid, with equal sides and rounded angles. 



2 z 2 



