TRANSACTIONS OF SECTION C. 



743 



done the position of the assemblage of organisms found near the base of the Saint 

 John group. The trilobites are taken as a criterion for this purpose. A brief 

 statement of the position and thickness of the beds is given, showing the relation, 

 of the fauna to the formation as a whole. 



It is shown that the genera and species of the Acadian trilobites do not agree 

 with those of the Menevian, in the restricted application of that term now in vogue ; 

 the great Paradoxides with short eyelobes, and the genera Anopolenus, Agraulos 

 ( = Arionellus),Erinnys, and Holocephalina being, so far as known, absent from it. On 

 the other hand, it shows very close relationships in its genera to the Solva group 

 fauna, especially in the following species : 



Solva Group. 



Conocoryphe solcensis (Hicks). 

 Conocoryphe bufo (Hicks). 

 Paradoxides Harknessi (Hicks). 



Acadian Fauna. 



Ctenocephalus Matthewi (Hartt sp.). 

 Conocoryphe olegans (Hartt sp.). 

 Paradoxides cteminicus (Matthew). 



As bearing on the question of the age of the Acadian fauna, the development 

 of the eyelobe in Paradoxides is referred to, and it is shown that while in the 

 Cambrian rocks of Wales the length of the eyelobe is in direct relation to the age of 

 the strata, the Paradoxides of the Acadian fauna, having continuous or nearly con- 

 tinuous eyelobes, are more primitive in their facies than those of the Menevian, 

 and agree with the species found in the Solva group. 



The family of Conocoryphidae, restricting the name to such species as those 

 described by Corda under Conocoryphe and Ctenocephalus, are a marked feature of 

 this early i'auna ; and Conocoryphe has a characteristic suture not observed in 

 the Menevian genera. The Acadian Ctenocephalus also differs in this respect from 

 the Bohemian species. 



2. The Primitive Conocoryphean. By G. F. Matthew, A.M., F.E.S.G. 



Relates to the development of the species Ctenocephalus Matthewi and other 

 Conocorypheans of the Acadian fauna, and is considered under the three heads, viz., 

 the Development of the Glabella ; the Acquisition of Sensory Organs ; and the 

 Decoration of the Test. 



Under the first head, it is shown that the peculiar glabella of the species above 

 referred to is closely related to the early history of the trilobite. The glabella, in 

 its earliest stage, is very different from that of the adult, and in outline is not 

 unlike that of Paradoxides : it also resembles this species in the position of the ocular 

 fillet. At the next stage the glabella or axial lobe becomes trumpet-shaped, as in 

 Carausia, and in the third the glabella proper is developed by the segmentation of 

 the axial lobe : the glabella and ocular fillets now resemble those of Ptychoparia. 

 In the following stages the family characters of the Conocorypheans begin to 

 assert themselves, especially the widening of the base of the glabella, the appear- 

 ance of the canals connected with the ocular ridges, and the development of spines. 



2. The Acquirement of Organs of Sense. — The ocular fillet appears, in the 

 second stage of growth, as a faint, narrow ridge, close to the anterior marginal 

 fold, and extending but a short distance from the glabella. It is not until the fifth 

 stage of growth that the ramifying branches which spread from the ocular ridge to 

 the anterior margin make their appearance. The ocular lobe and sensory apparatus 

 connected with it are more distinctly visible on the under than on the outer surface 

 of the test, and the canalets connected with the lobe spread over the anterior 

 slopes of the shield and extend to the anterior margin. In the tuberculated species 

 they connect by hollow spines with the outer surface. In one species they coyer a 

 wider space than in the others, extending some distance behind the ocular ridges 

 and over the front of the glabella. 



3. Decoration of the Test. — In all the Acadian species of this group but one, the 

 surface of the test at maturity is covered with tubercles and spines similar to the 

 surface-markings of Conocoryphe S'ulgeri, &c. In the earliest stages, however, no 

 6uch tubercles are foimd, but the surface appears smooth or scabrous. In Cteno- 



