6 



Belt — On the Fauna of the *' Lingula Flagt 



species of Trilobites from the Dolgelly and Tremadoc strata have 

 been separated from the Olenidce to which they naturally belong, 

 and placed with the Conocephalidce with which they have no affinity. 

 These pseudo-Conocoryphe have a thin and smooth crust and are flat 

 or but little convex. The pleurge are falcate and pointed, and only 

 slightly bent down at the fulcrum ; the axial furrows are shallow ; 

 the facial suture ends below, some distance within the posterior 

 angle. In all these points the pseudo-Conocoryphe approach the 

 genus Olenus. The typical species of Conocoryphe from the Lower 

 Cambrian rocks, on the contrary, are very convex and have a thick, 

 granulated, or even sub-spinous crust. The pleurae are strongly 

 bent down, so as often to be nearly vertical from the fulcrum ; the 

 axial furrows are deep ; the facial suture ends below, close to the 

 posterior angle, so that if the marginal furrow of the free cheek were 

 produced downwards it would cut the suture. In all these points 

 the typical Conocoryphe are distinct from Olenus and approach Caly- 

 mene. All the species of Conocoryphe from the Lower Cambrian 

 rocks belong to the typical group, and all the species that have been 

 referred by various authors to that genus from the Upper Cambrian 

 rocks belong to what I have called the pseudo- Conocoryphe ; I have 

 only retained them provisionally in Conocoryphe, because it is im- 

 possible without specimens of Angelin's species, or better figures of 

 them than he has given us, to determine whether they belong to his 

 genera Solenopleura, Centropleura, etc., or not. The whole of these 

 pseudo- Conocoryphe show so many points of affinity with Olenus that 

 in drawing up the following table of the Trilohita from the Maen- 

 twrog, Festiniog, and Dolgelly strata, I have had no hesitation in 

 including them amongst the Olenidce. 





Trilobites of the Maentwrog 



, Festiniog, and Dolgelly Groups. 



s 



1 



1 



1 



Species. 



Maentwrog 

 Beds. 



Lower. Upper. 



Festiniog 

 Beds. 



Lower. Upper. 



Dolgelly 

 Beds. 



Lower. Upper. 



Dikelocephalus ? Cellicus, Sal. ... 



„ ? discoidalisj Sal. 

 Conocoryphe ? abdita, Sal 















„ Hmita, Sal 



„ ? Williamsonu, n. sp. 



„ ? lonffispina, n . sp. . . . 



„ ?bucephala, n. sp. ... 



Olenus ffibbosus, Wahl 



„ truncatus, Ang 



,, cataractes, Sal 



Parabolina spinulosa, Wahl 



Peltura scarabceoides, Wahl 



Sphcerophthalmus ?iumilis, Phil.... 

 „ bisulcatus, Phil. 



Agnostus nodosus, Belt 



,, pisiformisy Lin 



„ „ var. obesus. Belt. 

 „ sp 



„ obiiisus, n. s^ 



„ princeps, Sal 



„ trisectus, Sal 



