BY R. ETHERIDGE, JUXR., AXD .TOIIX MITCHELL. 695 



The study of this group has proved au arduous oue from the 

 complex nature of the cephalic shield or cephalon, and we may 

 have erred by introducing too much detail; this is, however, au 

 error on the right side. 



" Of all the extravagant forms of this curious family of 

 Trilobites," says Salter,* "none seem so extravagant in its orna- 

 ment as the genus Acidaspis; the head, thorax, and tail being 

 literall}" crowded with spines wherever an available angle occurs." 



Genus Odon TOPLEU R A, Emmrich, 1839. 



Oc/oatopleura, Emmrich, De Trilobitis, 1839, p. 35. 



,, Burmeister, Organization of Trilobites (Ray Soc), 



1846, p. 61. 



,, Clarke, 10th Ann. Report State Geol. N. York for 



1890 (1891), p. 67. 

 Obs. — This genus is distinguished from other Acidaspids by 

 having the occipital ring either with or without a tubercle in the 

 centre, but totally devoid of a spine or spines. The type, 

 according to Mr. J. M. Clarke, is 0. ovata, Emmrich, a form 

 having some characters in common with our first species, but 

 in others departing widely from it. 



The specific history of the Acidaspidse in Australia is a brief 

 one. As recorded by Mr. F. Ratte,t Mr. Chas. Jenkins, L.S., 

 appears to have been the first to recognise the presence of the 

 genus in our rocks. He figured the greater portion of a Trilobite 

 that he referred to Acidaspis ^/'t^/t^tV, -Murchison, | from Yass, 

 but during our researches we cannot say that we have met with 

 any Trilobite that would strictly agree with that species; indeed 

 we have not seen a true Acidaspis, as now restricted, from Aus- 

 tralia. Mr. Jenkins was followed Ijy the late Mr. Felix Ratte, 

 who contributed two papers to the Proceedings of this Society 



* Brit. Org. Remains, Dec. vii. , Pt. 6, p. 2. 



t Proc. Liun. Soc. N.S. Wales, 1SS7, ii. (2), p. 99 (footnote). 



X Proc. Linn. Soc. N.S. Wales, 1879, iii., Pi. 17, f. 5. 



