68 



INTRODUCTION. 



unknown ; a mesial septum exists in the interior of smaller valve ; cardinal process large 

 and produced ; external surface plaited. 



Obs. It is still very uncertain whether this sub-section should be retained, or placed 

 under Waldheimia or Terebratella, from the mode of attachment of its loop not having 

 been as yet ascertained : the elongation of the beak could not alone constitute a character 

 of generic importance. M. d'Orbigny supposes that the loop was doubly attached, while 

 Dr. Gray seems to be of a different opinion, since he places the shell in question with 

 Waldheimia} It will therefore be very desirable to examine the interior of T. lyra, which 

 will alone decide whether the section should be admitted or cancelled. 



Geol. range.— ^\is, shells placed by authors into this small section seem, in the present 

 state of our knowledge, confined to the cretaceous period. 



Examples: T. lyra. Sow., sp. ; Bargesana, D'Orb. ; neocomiensis, D'Orb. ; &c. 



Section C. Megerlia, Khig, 1849.^ 



Type—U. TRUNCATA, Gmel. sp., 1152. Int., PI. VI, figs. 26, 27. 



Anomia (part), Linneeus, Pallas, &c. 

 Teeebratula (part), of the generality of Authors. 

 Orthis, Michelotti,^ Philippi,'^ (not ortiiis, Daltnan.) 

 Terebratella (part), D'Orbigny. 

 Megerlia, King, Gray, &c. 

 Megathyris (oblita), D'Orbig. 

 Kin gen A, Dav. (part). 



Shell inequivalve, suborbicular, transverse or longitudinally oval ; beak short and trun- 

 cated by a circular foramen ; deltidiura small ; beak ridges well defined ; external surface 

 smooth, spinulose, or covered by fine radiating striae ; shell structure largely punctated ; 

 hinge line sometimes long and straight, with the articulating teeth and sockets widely 

 separate. In the interior of the socket or dorsal valve a slightly elevated medio-longitu- 

 F'g- 11- Fig. 12. dinal septum proceeds from under the car- 



dinal process or boss, to less than half the 

 length of the valve ; the loop is three times 

 attached, first to the base of the socket 

 ridges, afterwards, by a horizontal process, 

 ,, ,„ „ ,. ..... J., , , s to near the extremity of the septum, and 



11,12. Megerlia truncata {interior of dorsal valve). '' r ' 



' A Catalogue of the Brachiopoda in the British Museum, 1853. 

 2 A Monograph of English Permian Fossils, p. 145, 1849. 

 ^ Desc. des Foss. des Terrains Miocenes de I'ltalie, sup., p. 78, 1847. 

 only a synonym of the M. truncata, Gmel. sp. 



* Enumeration Molluscorum Siciliae, vol. ii, 1844. 



The Orthis oblita, Mich., is 



