PELTURA. 95 



the glabella is very similar and the fixed cheek is about the same width, or perhaps 

 a little narrower, compared with the glabella. 



Horizon and Localities. — Upper Lingula Flags: Carreg-wen, Borth, Portmadoc. 



Genus PELTURA, Milne-Edwards. 



The genus Peltura was separated by Milne-Edwards 1 from the Paradoxides 

 of Brongniart mainly on account of the character of the tail, which he describes 

 as " scutiform and well developed." The type-species is the TUntomostracites 

 scarabseoides of Wahlenberg. 2 Milne-Edwards' description, like Wahlenberg's 

 figure, was apparently based on specimens in which the free cheeks were missing, 

 and accordingly he states that eyes are absent, and in well-preserved specimens 

 the latero-posterior angles of the cephalic shield are prolonged into horns. He 

 also appears to exaggerate the size of the tail; but otherwise his description is 

 accurate. 



The genus was subsequently more fully defined and more strictly limited by 

 Angelin. In his diagnosis the more prominent distinguishing characters are as 

 follows : Genal angles rounded, without spines ; glabella broad, reaching nearly to 

 the anterior margin, glabellar furrows faint; eyes small, set far forwards and close 

 to the glabella ; thorax of twelve segments, axis wider than the pleurae, pleurae 

 pointed ; tail small, with a toothed margin. 



There are, however, certain forms which do not completely agree with Angelin's 

 description, and which are yet very closely allied to Peltura scarabseoides. Thus 

 Brogger's Gyclognathus costatus in general resembles Peltura, but the glabellar 

 furrows are obsolete and the tail is entire. In Protopeltura acantkura, Broggeiy 5 

 the cheeks bear short spines. B nigger 4 accordingly was led to modify Angelin's 

 definition so as to include these forms, and he divides Peltura into Protopeltura 

 (with genal spines), Peltura proper (equivalent to Angelin's Peltura), and 

 Gyclognathus (with tail margin entire). 



Angelin's genus Acerocare also resembles Peltura in many respects. The genal 

 angles are rounded, the eyes set near to the glabella, and in the type-species, 

 A. ecorne, the number of thoracic segments is twelve. But in A. ecorne, at least, 

 the eyes are not so far forwards as in Peltura, the thoracic axis is narrower, the 

 pleurae are not pointed, the tail is larger and has an entire margin. 



1 Hist. nat. des Crustaccs, vol. iii, p. 344. 



2 Under the name Peltura buchlandi, Milne-Edwards also included in the same genus the " trilobite 

 de Dudley " of Brongniart. This, however, is a Lichas which has since been fully described and 

 figured by Fletcher as Lichas bucklamdi, Quart. Journ. Geol. Soc, vol. vi (1850), p. 235, pi. xxvii,figs. 

 1 — 5, and pi. xxvii bis. fig. 1. 



3 According to Moberg and Mtiller (Geol. Ffiren. Stockh. Forh., vol. xx (1898), p. 265) this is 

 not, as Brogger supposed, the Olenus ? acanthurusoi Angelin. The latter, they state, is a Pardbolina, 



4 Die Silur, Etagen 2 und 3, p, 105. 



