F. R. Cowper Reecl — Evolution of Chcir tints. 121 



the pleura, and the greater development of the articulating band 

 on the inner portion of the pleura. Closely allied forms are Ch. 

 iusocialis, Barr., and Ch. gryphus, Barr., of Dd 4 and Dd 5. In all 

 these above-mentioned species the basal lobe of the glabella is 

 incompletely separated, for the third glabellar side-furrow does not 

 unite with the neck-furrow. If we regard the head-shield as 

 composed of several fused segments, we must look upon this non- 

 union as a primitive feature. The presence of an anterior wing to 

 the fixed cheek not crossed (or only very feebly) by the marginal 

 furrow is also a noticeable character in all the Eccoptocheile group. 

 About this point the main stem seems to give off two branches 

 which lead to such diverse forms as Pseudosphcerexochus and 

 Crotalocephalus respectively. 



Turning first to the branch that ends in Crotalocephalus, we find 

 that we are leaving Section II of Schmidt and entering upon his 

 Section I through a considerable number of intermediate forms 

 linking Eccoptocheile with Cyrtometopus. The subgenus Cyrto- 

 metopits, with its rather heterogeneous and ill-defined characters, 

 first demands our attention. In it the number of eleven thoracic 

 segments, characteristic of Schmidt's Section I, with constricted 

 pleura?, is met with. The pleural groove is confined to the inner 

 portion of the pleura, and is longitudinal; the basal lobes of the 

 glabella are incompletely separated (except in Cyrto. ? pseudo- 

 hem icraninm, Nieszk., which belongs to a minor lateral branch) ; the 

 fixed cheek has an anterior wing not crossed (or only feebly) by 

 the marginal furrow just as in the typical Eccoptocheile. The type 

 of the subgenus is Cyrto. clavifrons (Dalm.). The pygidium varies 

 somewhat, but most commonly its anterior pleurae are enlarged and 

 project behind the posterior ones, which are of smaller size. There 

 are normally only three pairs of pleurae with free ends in the 

 pygidium, but the fourth pair is represented by a single median 

 terminal piece. 



Ch. juvenis (Salter), which was placed by its author in the 

 ill-defined subgenus Actinopeltis, has close affinities to a true Cyrto- 

 metopns in the characters of the head- shield and pygidium, but the 

 complete separation of the basal lobes from the glabella by the third 

 side-furrow is a distinguishing feature, and suggests an alliance with 

 Cyrto. ? pseudohemicranium (Nieszk.). The position of the side- 

 furrows and course of the facial suture in some specimens show 

 some similarity to those of Pseudosphcerexochus, but I strongly 

 suspect that two or more distinct species, and perhaps even different 

 subgenera, have been included under the specific title of Ch. juoenis. 



The two species Cyrto. ? pseudohemicranium (Nieszk.) and Cyrto. ? 

 aries (Eichw. sp.) may ultimately need the creation of a new sub- 

 germs intermediate between Cyrtometopus and the strange Sphcero- 

 coryphe. 



The reasons for the removal of these forms from other subgenera 

 are at present (1) the complete separation of the basal lobes by 

 the strong third glabellar side-furrow joining the neck-furrow, and 

 the smaller elevation of these lobes than the rest of the glabella ; 



