50 BRITISH CAMBRIAN TRILOBITES. 



0. praenuntius are longer than in 0. elatifrons, and, where they spring from the 

 cheeks they are often more strongly bent outwards. In both species the number 

 of thoracic segments may vary, even in forms which in other respects appear to 

 be adult. In 0. praenuntius none of the specimens have more than seven; in 

 0. elatifrons the few specimens which afford any evidence on this point have either 

 eight or nine. 



The type specimens of Salter's Ampyx praenuntius are unfortunately unknown, 

 and appear to have been lost ; but Salter states that in this form the glabella is 

 short and not produced to the margin, and there is a narrow convex rim around 

 the head. In these characters it agrees with Orometopus and differs from the true 

 Ampyx. The specimens were found at Pen-y-clogwyn, near Tremadoc ; and in the 

 Jermyn Street Museum there is a specimen from this locality which was labelled 

 Ampyx but which belongs to the species here described. Further, Mr. Fearnsides 

 tells me that the beds at Penmorfa, in which his specimens of Orometopus 

 praenuntius were found, may be traced to Pen-y-clogwyn, where the same horizon 

 is seen. There is, therefore, very strong presumptive evidence that the species 

 here described is identical with Salter's Ampyx praenuntius. 



Horizon and Localities. — Upper Tremadoc : Pen-y-clogwyn and Penmorfa, near 

 Tremadoc ; Ceunant-y-garreg-ddu and Ainnodd Bwll, Arenig. The Amnodd Bwll 

 specimens occur in material of the same character as the specimens of Shumardia 

 pusilla var. morvensis from the same locality. 



Family Olenid,e. 



(leu us OLENUS, Dalman emend. Angelin. 



The name Olenus was substituted by Dalman for the name Paradoxides 

 previously proposed by Brongniart, and the species which he enumerates are 

 nearly the same as those given by the latter author. The only exceptions are 

 that Dalman places in this genus the Entomostracites bucephalus of Wahlenberg 

 and removes the Entomostracites laciniatus of the same writer. Brongniart's 

 genotype was Paradoxides lessiui, and when it became necessary to divide the 

 genus, the name Paradoxides was limited to those forms in which the glabella- is 

 swollen in front, while Dalman's term Olenus was by common consent employed 

 for those in which the glabella is rectangular or parabolic in outline. Subsequent 

 discovery showed that even with this limitation the genus Olenus is too large and 

 varied to admit of satisfactory definition, and Angelin accordingly restricted it to 

 forms of the type of Olenus gibbosus and Olenus truncatus. The name, however, is 

 still very often employed in a wider sense, and the following table by E. Persson 1 



1 G-eol. Foren. Stockholm Fork, vol. xxvi (1904), p. 525. 



