110 G. F. MATTHEW: ILLUSTEATIONS OF 



in the number of spines covering the test, and the arrangement of these spines is less reg- 

 ular than in the younger heads. The number of spines usually found on shields of this 

 size is given in the i^receding table. 



Size 19 X 88 mm. {Fig. 6.) — In this, which may be considered the adult stage of this 

 species, the most notable features are the increased irregvilarity iu the number of the 

 spines, and the greater distinctness of the eye lobe and its ramifications. 



Resemblance of the Young Tests to Other Species. 



A:dal lobe. — The earlier stages of growth in this trilobite are of much interest, es- 

 pecially those which precede the second segmentation of the axial lobe of the cephalic 

 shield. In place of the conical glabella, which characterizes the Conocoryphea at ma- 

 turity, these ombiyonic tests have a club-shaped, or trumpet-shaped, median lobe, simulat- 

 ing, to some extent, the glabella of Paradoxides and Carausia, and especially the younger 

 stages of Sao kirsuta. As in the first named genus, the eyelobe begins opposite an anterior 

 enlargement of the axial lobe of the shield, and sweeps outward toward the genal angle. 

 The long genal spine of the early stages adds to the likeness. 



Frontal lobe. — The growth of this part is an interesting feature in the history of 

 this trilobite. At first it was a narrow segment cut off from the median lobe ; but as the 

 animal grew, and the eyelobe retreated from the front of the shield, a corresj)ondiug in- 

 crease in the length of this part took place ; until, from being when first seen about one- 

 fifth only of the axial diameter, it became at maturity nearly a third. What the glabella 

 lost in length during the growth of the animal, was partly acquired by this frontal pro- 

 tuberance of the shield. 



In the young of Conocor//phe Baileyi corresponding to the second and tliird stages of this 

 species, there is a slight protuberance in this part of the shield, so that in distorted young 

 tests it is not always easy to distinguish the two species ; especially in the second stage of 

 Ct. MaUhewi, when there are no tubercles visible and when the position and sweep of the 

 ocular ridge in the two species and in Conoconjphe elegans are very similar : but in the 

 older tests, in which the specific characters are more fully developed, the species are easily 

 separated. In the European Conocoryphe Sulzeri a slight protuberance of a similar nature 

 may be observed, but it does not assume importance. 



Arratigement of the spines (Fig. 9, Sfc.) — Although at the first glance the spines, which 

 are strewed over the surface of the test in this species, appear to be placed without order, 

 it is evident, on a more careful survey, that some at least are arranged in a definite way. 

 Several rows of spines may be observed, especially in the young, crossing the glabella ; 

 and the sxrrface of the test is sometimes seen, both in this s^iecies and in Conocoryphe ele- 

 gans, to be slightly elevated along the lines where these spines are set. It would appear 

 that some general purpose in the economy of these trilobites is subserved by the eleva- 

 tion of the test at these places. 



Glabella. — In this species (O. Matthewi), the glabella is relatively smaller than in any 

 other of the Conocorypheans occurring at St. John ; and it does not fairly assume the 

 form characteristic of the genus until the shield has attained half of its largest diameter. 

 This will be seen by the following table. In this table the measurement of the small 

 shields are only roughly approximated : — 



