BY R. ETIIERIDGE, JUN., AND JOHN MITCHELL. 177 



arched backwards laterally and forwards in the middle line ; 

 thoracic spine absent ; axial grooves well marked ; pleurai 

 straight, flat above, distal ends sharply bent downwards, furrows 

 wide and barely reaching the outer margin. Pygidium small, 

 transversely elongated, widely triangular, its transverse measure- 

 ment three times that of the axial length ; coalesced segments of 

 the pleurse invisible ; axis prominent, short, truncated posteriorly, 

 of seven or eight segments, the terminal ones very close together ; 

 limb very abruptly depressed, flat. 



Ohs. — This little Trilobite, in its short pyriform glabella and 

 circumscribed lobes, assumes the habit of Cyphasjns ; the shape 

 of the thorax generally approaches more closely that of the genus 

 Proetus, whilst the pygidium in its dimiautive size is again of a 

 Cyphaspis type. Its rotund appearance at once separates it from 

 the preceding species and the European C. megalops, and this 

 separation is further increased by the presence of comparatively 

 short genal spines. Fi'om the other Australian species it is 

 distinguished by possessing eight instead of eleven or twelve 

 thoracic segments, the rotund outline, and in the length of the 

 cephalic-shield equalling that of the combined thorax and pygi- 

 dium. From Cyphaspis depressa, Barr.,"^ C. Halli, Barr.,t and C. 

 Burmeisteri, Barr.,| it is distinguished by having no trace of a 

 thoracic spine, but if there is a possibility of this point of 

 differentiation being of a sexual nature, as previously suggested, 

 the characters mentioned above will serve foi- the purpose in 

 view, particularly the almost oval shape and closely adpressed 

 genal spines. 



Loc. and Horizon. — Bowning, Co. Harden — Lower Trilobite 

 bed, Bowning Series (? Wenlock) (Coll. Mitchell). 



* Syst. Sil. Boheme, 1852, i. Atlas, t. 16, f. 38, 39. 

 f Syst. Sil. Boheme, 1852, i. Atlas, t. 18, f. 35. 

 X Syst. Sil. Boheme, 1852, i. Atlas, t. 18, f. 61. 



12 



