PHILLIPSIA. 11 



Family PROETID^. 



This family comprises tlie one Silurian genus Peoetus,^ and tlie three Carboni- 

 ferous genera — Phillipsia, Griffithides, Brachymetopits, which form the subject of 

 our present memoir. 



Genus I. — Phillipsia, Portloclc, 1843. 



Greneral form oval ; glabella with nearly parallel sides, marked by either two 

 or three short lateral farrows ; the posterior angles, forming the basal lobes, always 

 separated by a circular furrow from the rest of the glabella ; eyes large, reniform, 

 surface delicately faceted f cervical furrow deep ; free cheek separated from the 

 glabella by the axal suture which forms an acute angle with the circular border of 

 the cheek in front of the glabella ; whilst the facial suture cuts obliquely across the 

 posterior margin, just behind the eye, leaving a small pointed portion fixed to the 

 glabella by the neck-lobe ; angles of cheeks more or less produced, margin of head 

 incurved forming a striated and punctated rim. Thoracic segments nine in 

 number, the axis distinctly marked off from the side-lobes or pleurae by the axal 

 furrows ; the abdomen, or pygidium, usually with a rounded border, the axis 

 composed of from 12 to 18 coalesced segments. 



The following is General Portlock's description of the genus niillipsia, taken 

 from his ' Report on the Geology of Londonderry, &c.' (8vo. 1843, pp. 305, 306). 



" General form, oval. Cephalo-thorax divided into three compartments by the 

 elevation of the glabella above the plane of the cheeks. Glabella, bounded on the 

 sides by nearly parallel lines, and rounded in front ; the general form approaching 



1 M. Barrande suggests that Dr. Sandberger's genera Trigonaspis and Cylindraspis, from the 

 Devonian of Nassau, also belong to the genus Proetus. Prof. Dr. Perd. Eoemer has figured and 

 described four species of Proetus from the Ilarz, and Messrs. Meek and Worthen have named a species 

 Proetus from the Lower-Carboniferous series of Jersey Co. Illinois, so that Proetus serves to connect 

 this otherwise detached group of Mountain-Limestone forms with their relatives in the Silurian and 

 Devonian formations. 



2 Messrs. Meek and "Worthen, in their description of two Carboniferous Trilobites from Illinois 

 and Indiana, remark, " eyes apparently smooth, but showing, when the outer crust is removed, numerous 

 very minute lenses beneath," ' Geol. Surv. Illinois,' vol. v, "Paleontology," 1873, 4to, pp. 528, 529. 

 This observation may serve to explain the fact that many specimens do not show the faceted surface 

 at all clearly ; this is especially the case in the genus Oriffithides. Emmrich believed it possible to use 

 this character of the external surface of the eyes of Trilobites as a means of classification, but I have 

 not been able to accept his proposed arrangement based on this structure, (See Emmrich, op. cit., 

 1845, in " Bibliography," p. 5.) 



