102 G, F. MATTHEW: ILLUSTRATIONS OF 



IL— CONOCORYPHEA. 



In Professor Hartt's descriptions of the species of the St. John group, ("Acad. GcoL," p. 

 648, etc.,) he has grouped together, under the genus Conocej^halites of Barrande, a large 

 number of species which would now be divided among several genera. When tested by 

 the criterion of the eye-lobe it will be observed that they all belong to one or other of two 

 groups, — one characterized by the possession of eye-lobes and free cheeks ; the other consist- 

 ing of trilobites which apparently have no eyes, and have a suture which cuts off only a 

 poi'tiou of the rim of the head-shield. This latter group is the one which I propose to 

 make the subject of this article. 



The Conocoryphea, as thus limited, appear to be confined to the lower plane of the pri- 

 mordial zone, and are thus almost as characteristic of this horizon as Paradoxides itself In 

 their younger stages, the trilobites of this group assimilate in general form miich more 

 closely to the eyed Conocephalites than they do when they approach maturity. This resem- 

 blance is chiefly due to the narrowness and comparative great length of the glabella in the 

 young of the Conocorypheans, — a peculiarity which disappears in the later stages of growth, 

 for in these stages the glabella contracts in length and expands at the base, and finally as- 

 sumes that conical shape to which this form of trilobite owes its name. 



In the group of trilobites of this sub-family which is found in the Acadian region, some 

 points of structure come into view which are not evident in the corresponding species of 

 the Old "World, and raise the question as to whether too much weight has not been attached 

 to the course of the facial suture as a means of dividing genera. Thus, in regard to the 

 two species Conocoryphe Suheri and Ctenocephahis Barrnndd of Corda, ( Conocephalites 

 coronaius, Barr.) associated together by Barrande in the genus Conocephalites, he mentions 

 that the suture in the two species is the same in position, and takes the ground that the 

 differing number of segments in the thorax and the diverse pygidia are not of sufficient 

 value to carry these species into different genera, and therefore that Corda should not be 

 followed in thus dividing them. 



I think, however, it will be made clear from the additional light thrown upon the 

 relations of these two species by a knowledge of the life-history and the mature features 

 of Conocephalites Mallhewi (Hartt) that Corda was right in establishing two genera for these 

 species. It cannot be questioned but that the relationship between the last named trilobite 

 and Ct. coronatus is much closer than its connection with C. Sulzeri, and that this relation- 

 ship is most strongly shown in the possession by the two former of a marked protuber- 

 ance, or lobe, in front of the glabella, and by their small ijygidia. The value of the 

 protuberance, or frontal lobe, in discriminating the two genera is better appreciated 

 when the embryological development of Ct. Mattheioi is considered ; for it will be found 

 that this species springs from a more elementary form that the other Conocorypheans of 

 the St. John group, which by their pygidia and the form of their cephalic shield find their 

 relationship with C. Sulzeri, C. bufo, etc. Barrande remarks that the difference of one 

 joint in the thorax between Ct. coronatus and C. Sulzeri is not of sufficient moment even 

 when coupled with the existence of diverse pygidia to separate these two species generi- 

 cally. His opinion, as regards the lower generic value of the number of segments in the 

 thorax, is suiiiiorted by the fact that Ct. Matthewi possesses in the only known thorax but 

 fourteen segments, the normal number of segments in Ct. Svlzeri, but not in Ct. coronatus. 



