BY R. ETHERIDGE, JUN., AND JOHN MITCHELL. 319 



the Cyphaspis type, in which it agrees with P. decorus, Barr.,* 

 P. striatus, Barr.,f P. archiaci, Barr.| It, however, retains its 

 connection with Proetus by possessing eight thoracic segments. 



The nearly complete isolation of the basal lobes also separates 

 P. austrcdis at once from P. bowningensis and P. Rattei. 



The genal spines are of great length, embracing the whole of the 

 thorax, a marked increase in this particular structure on that of 

 P. bowningensis and P. Rattei. Herein P. australis agrees with 

 P. Loveni, Barr.,§ and a similar length of spine occurs in P. 

 Stokesii, Murchison, for McCoy || describes the genal spines of this 

 species as extending to the pygidium, and thus embracing the 

 whole of the thoracic segments. 



Loc. and Horizon. — Bowning Creek, Bowning, Co. Harden 

 (Coll. Mitchell) ; Lower Trilobite Bed of the Bowning Series — 

 Upper Silurian (? Wenlock). 



In our next communication we shall treat of the Genus Cyphaspis. 



EXPLANATION OF PLATE. 



Proetus bowningensis, Mitchell. 

 Fig. 1. — A specimen wanting the free cheeks and genal spines. 

 Fig. la. — A similar one with less of the glabella preserved. 

 Fig. lb. — A more or less complete individual. 

 Fig. ] c. — Side view of Fig. lb. 



Proetus Rattei, Eth.,fil., and Mitchell. 



Fig. 2. —The left half of a somewhat curved individual, showing the large 

 third thoracic pleural spine, -x 2. 



* Syst. Sil. Boheme, 1852, Atlas, t. 17, f. 13. 



t Syst. Sil. Boheme, 1852, Atlas, t. 17, f. 46. 



t Syst. Sil. Boheme, 1852, Atlas, t. 17, f. 42. 



§ Syst. Sil. Boheme, 1852, Atlas, t. 16, f. 25 and 26. 



II Brit. Pal. Foss., 1851, Fas. 1, p. 174. 



