Description of the Fossils in the older Deposits of the Rhenish Provinces. 369 



valve. The S. Burtini is very abundant at Paffrath, at Villmar, and in the Eifel. It is found also at 

 Dletz, Brilon upon the Lahn, at Chiniay, and in Devonshire. 



2. Strygocephalus dorsalis, Goldf. Bonn Mas. Tab. nost., XXXV. f. 5, 5 a. 



This species, named by Goldfuss, differs from the preceding only in having a more or less distinct me- 

 dian groove upon each valve. This groove is prolonged to the beak of the dorsal valve, and on thecon- 

 trarj' only reaches the middle of the ventral valve. Very delicate, slightly undulated, longitudinal strize, 

 which cover the whole shell and descend from the beaks to the edge of the valves, do not exist in the ^S*. 

 Burtini ; and the cardinal line, instead of being regularly arched, is formed of two straight lines, which 

 unite under the beak and present a very obtuse angle. 



Paffrath ; common ; Devonshire. 



Pentamerus Knightii, Sow. Min. Conch., PI. XXVIII. Murch. Sil. Syst., PI. VI. f. 8, &c. 



Contrary to the opinion of de Buch, who unites the Pentamerus to the Terebratula Gryphus, (Mem. 

 Geol. Soc. de France, t. iii. p. 174-) we think they ought still to be distinguished. The P. Knightii never 

 has the elongated form of the T. Gryphus, nor the pointed beaks where the cardinal edges meet at an 

 angle of 40°. We refer to P. Knightii some siliceous casts from the grauwacke of Greifensten in West- 

 phalia, and from Hohenzolen. 



1 . Spirifer curiatus, Terehratulithes curvatus, Schlot. Petrefact., PI. XIX. f. 2. 

 According to Mr. Hasbach this species is found at Paffrath. It exists also in the Eifel. 



2. Spirifer aperturatus, Terehratulithes aperturatus, Schlot. Petref., PI. XVII. f. 1. Trigonotretra apertu- 



rata, Bronn, Leth. Geog., PI. II. f. 13. Delthyris canalifera, Goldf. Bonn Mus. D. aperturata, de 

 Buch, Mem. de la Soc. Geol. de France, t. iv. pi. XIII. f. 19. Varieties, Tab. nost., XXXV. var. a. 

 f. 7, 7 a, and var. b. f. 8, 8 a. 



Bronn unites this species to the Terebratula canalifera, Lam., to make his Trigonotreta aperturata. 

 The height and the form of the area are variable, and the beak of the dorsal valve is more or less re- 

 curved. We shall particularize the two following varieties. 



Var. a. cuspidata, f. 7, 7 a. Area flat, perpendicular to the hinge, and forming a rectangular triangle 

 whose hypothenuse is the hinge itself. The general form of the shell is like that of S. cuspidatus (Sow. 

 Min. Conch., Tab. CXX.), from which, however, it is distinguished by having numerous folds in the 

 sinus and on the varix (which are wanting in the species of the mountain limestone), and in the greater 

 number of its lateral folds. Between this variety, which appears to remain of a small size, and the type 

 of the species, there exists an uninterrupted series of intermediate forms, in which the area has a ten- 

 dency to become concave, and the valves to assume larger and larger proportions relatively to this part. 

 The number of folds, however, remains the same. 



Refrath, and at Paffrath ; as casts. 



Var. b. echimdata, f. 8, 8 a. The form of this is the same as that of the common variety ; the area is 

 very elevated, its height being two-fifths of the length of the hinge. This shell is well characterized by the 

 small spines with which the folds are covered, the grooves which separate them remaining smooth. These 

 spines are short, truncated, close-set, and all directed downwards, thus giving to the folds some resem- 

 blance to certain spines of Cidarites. There are thirty folds on each side of the varix and of the sinus, 

 and twenty upon each of these last-mentioned parts. They are, therefore, finer and nearly double the 

 number of those of the other varieties. The sinus is also less deep and the varix less salient, and its folds 

 bifurcate more frequently than on the sides. 



Bensberg. 



De Buch unites the Terebratula subconica (Conch. Anomites subconicus, Mart., Petrif. Derb. Tab. 

 XLVIT. f. 5-7.) and S. bisulcatns (Sow. Min. Conch. Tab. CCCCXCIV. f. 1, 2.) to the S. aperturatus. 



