TRANSACTIONS OF SKCTION C. 



743 



^one the position of the assemblago of organisnis found near tlic baso of tbe Saint 

 Jol'.u fri'oiip. The trilobitos are taken as a criterion for this purpose. A brief 

 statement of the position and thickness of the beds is given, showinj,'' the relation. 

 of the fauna to the formation as a whole. 



It is shown that the genera and species of the Acadian trilobitos do not apreo 

 with tliose of tlu! ^Nlenevian, in the restricted application of that term now in vf)^iio ; 

 the peat Partido.vides with short eyelobcs, and the pentra Aunpolcnus, A(jniul(>.'i 

 ( = Arimelhis) ,Ennniif, and Ilolncc^t/ta/ina being, so far as knowr., absent from it, f )n 

 the utlii'i' hand, it shows very close relationships in its genera to the yolva group 

 fauiiii, especially hi the following species : 



Sol Lit Gro7tp. 



Conncuriiphc ■•^nlrenfis (llicks). 

 Cvihironjj)])!- Iitifo (Hicks). 

 Paradoxides ILirknessi (Ilicks). 



Acadian Fauna. 



Ctcnorephahi>t Matthevi (Ifartt sp.). 

 C'linomryphe uleyans (Ilartt sp.). 

 Paradoxidi'ii ctcminicus (Matthew). 



As liearing on the question of the age of the Acadian fauna, tlu' development 

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

 Cambrian rocks of Wales the length of the eyelobe is indirect relation to the age of 

 the strata, the I'aradiixides of the Acadian fauna, having continuous or nearly con- 

 tiiuious eyelobes, are more primitive in their fades thau those of the Menevian, 

 and agree with the species found in the Solva group. 



Tlie family of t'onoccryphidte, restricting the name to such species as those 

 deMTihed by Corda under Vi>n<iciir]i))lic and C/rn()cpp/ialii», are a marked feature of 

 this early fauna ; and Conontryplic lias a characteristic suture not observed in 

 the Menevian genera. The Acadian C'tcnucephalus also diilers in this respect from. 

 the Bohemian species. 



2. The Primitive Couocoryphean. By G. F. M.vttiikw, A.]\r., F.H.S.C. 



IJelates to the development of the species Ctcnocpphalvs Matthcivi and other 

 C'oiiocorypheans of the Acadian fauna, and is considered under the three heads, viz., 

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

 Decoration of the Test. 



Under the iirst 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 

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

 unlike tliat of Paradoxidcn : it also resembles this species in the position of the ocular 

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

 ('(iraimia. and in the third the glabella ]n-oper is developed by the segmentation of 

 tlie axial lobe: the glabella and ocular lillets now resemble those of rtychoparia. 

 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 Oryans of Sense. — The ocular fillet appears, in the 

 second stage of growth, .-is a faint, narrow ridge, close to the anterior margijial 

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

 stage of growth that the ramifying branches whieii syu-ead from the ocular ridge to 

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

 eounected 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 th(> anterior 

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

 they connect by hollow s])ines 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. 



;>. Decoration of the Test. — In all the Acadian species of this group biit one, the 

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

 surraee-marldnga of Conocoryphe Snlyeri, Sec. In the earliest stages, however, no 

 such tubercles are foiuid, but the surtace appears smooth or scabrous. In Cteno- 



