Description of the Fossils in the older Deposits of the Rhenish Provinces. 409 



Sp. macropterus. A third species is found at Schonecken in the Eifel, which differs from S. micropterus 

 in having no furrows near the edge of the central lobe in the cast of the interior, and in the straightness 

 of the septa which form that lobe. 



We might be easily led to adopt the structure of the parts about the hinge as of sufficient importance 

 for generic characters, but these shells, and many others, show us that such distinctions would be purely 

 artificial, and could only be employed safely when they occur constantly in union with several other 

 characters. 



Fig. 7. Orthis ? strigosa. Semi-elliptical, longer than wide, flat, with numerous strong, alternately 

 large and small striae ; muscular impressions very shallow, approaching those of Leptcena. We have only 

 one valve of this sharply striated shell ; the hinge, teeth, and septa are very small. Loc. Haiger Stilbach 

 (Dillenburg). 



Fig. 8. Orthis virgulata. Orbicular, with a pointed beak, convex, striated ; striae numerous, very re- 

 gular, and continued to the beak ; septa within the beak large. Loc. Haiger Siilbach. 



Fig. 9. Orthis Pecten? (Silurian System, 638, pi. 21. fig. 9). The specimens are very defective, 

 the name is therefore given with doubt (fig. a, portion of the hinge of a Spirifer). 



Fig. 10. Orthis obovata. Obovate, depressed, beak-pointed ; margin internally striated; hinge-line 

 short ; septa long ; muscular impressions united, large. Loc. Haiger Siilbach. 



Fig. 11, Orthis partita. Semi-elliptical, longer than wide, very convex ; beakshort, divided by a cen- 

 tral septum ; internal margin ribbed. This has several characters in common with Leptcena. Loc. 

 Haiger Siilbach. 



Fig. 12. Orthis circularis. Orbicular, flat?, margin striated within ; beak very small ; hinge-line and 

 septa very short ; muscular impressions flattened. The larger (convex ?) valve unknown. Loc. Daun, 

 in the Eifel district. 



Fig. 13. Leptana {Producta}) profunda. Subcylindrical, regularly striated or ribbed to the apex; 

 front very long ; edge oblique, elliptical. A very curiously formed shell. If I comprehend it rightly, it 

 is a Leptaena of the same division as those species which are typical of the genus Producta, and which 

 are distinguished by the great length of the descending front ; it however differs in the form of the 

 prominent beak-like projection seen in the cavity of the cast, in the regularity of the striae and the 

 total absence of spines. When the structure of the shells of this family is better known, Producta and 

 LeptoEua may prove two good genera, and the fossil before us may become the type of a new genus. 

 Loc. Olpe. 



Fig. 14. LeptcBua semiradiata. Semicircular, twice as wide as long, convex, marked with twenty-five 

 or thirty even radii, which extend about half over the shell and are then lost ; the rest of the surface is 

 smooth, or only marked with lines of growth ; under valve concave externally. This resembles L. sericea, 

 and Z. Lepis in form ; it has short spines on the hinge-line like L. lata, but from all these is distinguished 

 by the elegantly radiated surface. Specimens occur in the Eifel twice the length of the figures. Loc. 

 Priim, Daun, Eifel. 



(a.) Cast of the outside of the convex valve. 



(b, b, b.) Cast of the inside of the same valve. 



(c.) Cast of the outside of the concave valve. 



(d.) Cast of the inside of the same valve. 



(c.) Outside of the same valve, with the calcareous substance of the shell remaining. 



Fig. 15. Leptcena explanata. Half-obovate, nearly as long as wide, flat, irregularly and finely striated. 

 This is a cast of the lower or concave valve, and has the minutely pitted surface and usual characters 

 of Leptcena well-marked. 



On the same mass are imperfect casts of Terebratula Stricklandi ? 



