Description of the Fossih in the older Deposits of the Rhenish Provinces. 373 



Trigonia ? sulcata, Goldf., Tab. nost., XXXVII. f. 6. (See the Note, p. 400.) 



We preserve to these bivalve casts the name which Goldfuss has given them, undoubtedly from better 

 specimens than ours, for we should have been led to think them Cypricardice. They are, however, very 

 characteristic of the grauwacke of the banks of the Rhine. Those which we have from Ems appear to 

 differ in some respects from that of Kemmenau, which has been figured. 



Ems, Kemmenau ; common. 



Posidonia mytiloides, Goldf. 



Under this name we know a small shell of which impressions alone are found in the slates, and which 

 we have been unable fully to determine. It has also been given under the name of P. myacea. 

 Eibach near Dillenburg. 



Avicula Goldf ussii, nob., Tab. nost,, XXXVI. f. 15, 15 a. 



Shell subtrapezoidal, elongated, very inequilateral, thick, with a keel on each valve, which sets off 

 from the beak, and takes a tortuous direction toward the lower angle. Another, less distinct keel, 

 is placed a little lower, between the former and the cardinal edge. Beaks subterminal, small and 

 very recurved. Hinge straight, rather long and very oblique. Numerous and distinct lines of 

 growth covered the whole shell, and as far as we can judge from the cast which we have represented, 

 they were much finer and more close-set near the beaks. 

 The absence of all traces of teeth in the hinge, has prevented us from placing these casts among the 

 Pernce, with which they have some analogy in form and thickness. This shell is allied to the O. Saturni 

 of Goldfuss, PI. 116. f. 3. 

 Paffrath; rare. 



Area Michelini, nob.. Tab. nost., XXXVI. f. 6. 



Shell transverse, subquadrilateral, very inequivalve and ventricose. Beaks subterminal, i-ounded and 

 recurved. Hinge straight. Lower edge parallel with the hinge. Keel very much rounded, setting 

 off from the hinge and becoming attenuated as it takes a direction toward the lower posterior edge. 

 Striae of growth numerous, distinct, unequal, and slightly undulated. 



This species resembles Area torulosa, de Buch (IJber Goniatites und Clymenien in Schlesien, PI. I. 

 f. 12.), but the beaks are more rounded and more recurved, and the shell is more ventricose. 



Paffrath ; rare. 



Megalodon. 



The species of this genus, so numerous, and spread through the beds of Paffrath, are rare everywhere 

 else. There is one at Sotenich, and another ill-defined species has been found at Villmar ; and lastly, at 

 Newton and Bradley in Devonshire is found the M. eucullatus, Sow., Min. Con. Tab. DLXVIIL, which 

 is still much more abundant at Paffrath. 



Megalodon eotieentricus, nob.. Tab. nost., XXXVI. f. 11, 11 a. 



Shell reniform, very depressed, covered with regular, but indistinct, concentric folds. Beaks subter- 

 minal, very small, and recurved. Hinge of the left valve having one much flattened cardinal tooth, 

 divided by a shallow groove. Beyond a second groove which limits this tooth begins a fold, the 

 prolongation of a posterior lateral tooth, which is arcuated, very much elongated and equally divided 

 by a groove, toward the middle of which there is a little pit. Upon the right valve the hinge 

 presents but slightly different characters. A long narrow lateral tooth corresponds to the pit of the 

 other valve. Anterior muscular impression very distinct, oblong, striated, and placed under the 

 beak against the cardinal tooth. Posterior muscular impression unknown. Ligament subinternal. 

 Length, 75 millim.; width, 55; thickness, 12. 



VOL. VI. — SECOND SERIES. 3 C 



