72 DEVONIAN FAUNA. 



Class— LAMBLLIBRANCHIATA, Blainville, 1814. 



The abundance of bivalves in tbese beds is marked, though except in a few- 

 cases it is rather in the form of a variety of species than a profusion of individuals. 

 In some cases, especially in the Marwood zone, specimens occur in crowds ; for 

 instance, Gucullsea unilateralis, Sowerby, and Ptycliopteria Dam^ioniensis, Phillips, 

 sp., are evidently gregarious, while Prothyris scalprata, n. sp., completely covers 

 one rock-surface. In the Marwood beds, however, the number of species is few ; 

 but as we advance into the Pilton Zone we find, though shells are fewer, species 

 are greatly increased ; and there, though some are found commonly, most are only 

 known by one or two examples. 



Sixteen species were quoted from this area by Phillips, but of these, five seem 

 only synonyms. On the other hand, many of his South Petherwyn species are 

 found also to occur here. Not a few of the fresh forms bring out the relationship 

 to the American Devonians, and it seems remarkable how often light has been 

 thrown on our English species by the resemblance, not generally amounting to 

 specific identity, of Transatlantic shells. 



1. Obder— DESMODONTA, Neumayr, 1883.^ 



I. Family — PR^CARDiiDiE, Rudolf Homes, 1884. 



1. Genus — Panenka, Barrande, 1881. 



This genus being known only by its external characters, its position is 

 doubtful. Fischer includes it and its congeners, Prgecardhim, &c., in a provisional 

 family of his sub-order Anatinacea ; Neumayr (1891) places it under his order 

 Palseoconcha, Beushausen under Gardioconcha, Zittel under Homomyaria. Pos- 

 sibly its rightful place will ultimately be found to be near some genera now 

 included in the enlarged order Desmodonta. 



1. Panenka anglica, n. sp. Plate VIII, figs. 10, 11, 11 a. 



Descrijption. — Shell large, transverse, convex. Umbo small, incurved, facing 

 forward, and situated at about the anterior third of the length. Lunule large but 

 undefined. Surface covered by 35 or 45 regular, even, close-set, rounded rays, of 



^ Neumayr's classification has been mainly adopted by Zittel in his ' Pal<eozoologie,' 1895, who is 

 followed here. 



