BY R. ETHERIDGE, JUN., AND JOHN MITCHELL. 173 



fuirows terminating just short of tlie distal ends, which are 

 rounded. Pygidium semielliptical ; axis distinct, terminating 

 below in a tolerably sharp apex ; first three segments distinct, 

 others less so, the last two or three becoming very faint ; pleurje 

 of five coalesced segments, the anterior pair perceptibly furrowed, 

 the second and third pairs faintly so ; they terminate at the 

 margin ; limb striate. 



Ohs. — Cyphasjns yassensis is remarkable in possessing features 

 that distinguish several genera of Proetida3. Its wide limb, and 

 particularly the wide anterior glabellar border, relate it to 

 Arethusina ; its pyriform and tumid glabella allies it as strongly 

 to Cyphasjyis ; whilst, on the other hand, the proximity of the 

 eyes to the glabella and the small fixed cheeks are characteristic 

 of Froetus. The ])ygidium also approaches the latter type ; but 

 even the glabella is narrower and more pyriform than in generally 

 seen in Cyphasins. 



The glabellar furrows are as a rule not observable, but in one 

 fairly well preserved head-shield all three pairs are faintly visible. 



Amongst Australian Trilobites this species is the only one in 

 which the supposed auditory organs have been observed, and on 

 that account is of more than ordinary interest. The occurrence 

 of these pores, usually one on each side of the glabella, either in 

 the axial grooves or at any rate close to them, has been noticed 

 in several genera by various writers. The question has been 

 summed up by Dr. H. Woodward, "^^ who after instituting a com- 

 parison with the living genus SeroUs, believes that the pores in 

 question may represent either a simple eye, a tympanum, or an 

 olfactory organ; but it is still an open question which of the three 

 is the most probable. Such pores have been seen in the genera 

 Trinucleus, Ampyx, Griffithides, Phillipysia, Acidaspis, Calymene, 

 Cheirurics, and to these we can now add Cyp)has2ns. In our 

 Trilobite the pores, or, from our specimens being denuded of the 

 test, papillae, are not situated in the facial sutures, but between 

 them and the front rounded border of the glabella. 



* Moil. Brit. Carb. Trilobites (Pal. Soc), 1884, pt. 2. 



