ANIMALS. 145 



Genus Megerlia} King. 



Diagnosis. — A transversely-oblong, uni-areagerous Terebratulidia. TJmhone very 

 slightly projecting. Fissure or foramen large, emarginate, and situated in the centre 

 of the area. Cardinal muscular fulcrum excavated. Loop somewhat quadrate ; confined 

 to the posterior half of the shell; attached posteriorly to the crural base, and anteriorly 

 to the medio-longitudinal plate. Inner surface of valves radiately pimpled. Punctures 

 large. 



Type Anomia truncata, Gmelin. 



The species just noticed is included by M. d'Orbigny in Terehratella ; but as it 

 manifestly possesses a generic character of its own, I have been induced to consider it 

 as typifying a distinct (and in appearance a widely separated) genus. Perhaps the 

 proper position of Megerlia is in the family Bhgnchorida. 



Genus Waldheimia,^ King. 



Diagnosis. — A smooth or widely plicated, longitudinally-oblong Terebratulidia. 

 TJmhone projecting ; and truncated with a rather large forawien, which is bounded 

 inferiorly by a bisected deltidium. Loop forming a nearly complete ellipsis ; projecting 

 considerably into the cavity of the shell ; deeply folded back on itself so as to nearly 

 reach its crura ; and attached simply to the crural base. Labial appendages attached 

 to the loop throughout their entire length. Punctures large. 



Type Terebratula Australis, Q-uoy et Gaymard. 



Waldheimia differs from Terebratula in the form of the loop, and the character of 

 the labial appendages,^ both of which structures, in the former, are intimately connected 

 with each other, the loop supporting the labial appendages throughout their entire 

 length ; whereas in the latter, these organs project considerably beyond a small 

 anneliform apophysis, which mainly serves as a visceral support. The loop in the 

 typical species of Waldheimia, owing to its being so deeply recurved, is in the form of 

 a double ellipsis ; and it projects about two thirds of the length of the shell. 



Several Jurassic Terebratulidce appear to belong to the present genus. 



^ This genus is dedicated to the author of a paper entitled ' Entwurf eines neuen Systems der Schaalthiere 

 von J. K. Megerle v. Muhlfeld,' in the Freunde zu Berlin, &c., 1811. 



2 This genus is dedicated to His Excellency Fischer de Waldheim, to whom we are much indebted for 

 several valuable contributions on the Palaeontology of Russia. 



2 There is evidently a wide difference between Waldheimia and Terebratula in their labial appendages ; 

 but I am not prepared at present to enter on the subject. 



