110 HORN EXPEDITION PALEONTOLOGY. 



Hyulithes. Total length of hinge-line, 9 nnu.; umbo, 1'5 mm. from the front; width 

 of 2Jo.sterior margin, 3 nnu. 



Loc. — In limestone, Tempo Downs. 



Conocardium, sp. ind. (Phite II., Fig. 13.) 



The fossil here represented is a cast, which by its shape may possibly be 

 referable to Conocarditiiii. 



Loc. — In limestone, Tempe Downs. 



Class Bkachiopoda. 



Orthis leviensis, Eth., tils. 



Ref. — ii., p. 13, t. 1, tigs. .5-7 ; v., p. G, t. 1, figs. 2-5. 



Loc. — In limestone, Ilpilla Gorge, Middle Valley, Petermann Creek, Laurie's 

 Creek, north of Tempe Vale, Mereenie Bluff, and Horn Valley. 



Opthis dichotomalis, sp. nov. (Plate II., Figs, -l^a-d.) 



sp. char. — Shell s(!micircular, about twice as wide as long, the greatest width 

 at the long straight hinge-line ; cardinal extremities prolonged into acute, angular, 

 mucronate wings; valves concavo-convex. Ventral valve slightly concave, with a 

 deep depression along the middle, flanked on each side by a slight radial depres- 

 sion ; umbo sharp, pointed, but not prominent. Dorsal valve moderately convex, 

 with a median elevation, flanked on each side by a slight radial elevation ; umbo 

 insignificant and depressed. Hinge-line linear, concave, angular, sculptured with 

 parallel incised lines. Fissure rhombic, divided medially by the obtrusion of the 

 cardinal process of tlie dorsal valve, partially arched over by a pseudo-deltidium 

 adnate to each umbo. 



The ornament consists of slender radial threadlets, increasing in number by 

 successive dichotomising, about five in a width of 1 nun. at the medial front 

 margin ; the interspaces are crossed by tine distant growth-lines. Length, 16 mm. ; 

 width, 30 nun. ; sectional diameter, 3"5 mm. A very large specimen has length 

 17 nnu., width 35 mm. 



Loc. — Abundant in limestone, at Laurie's Creek, al.so at Petermann Creek, 

 noith of Tempe Vale, and Mereeuie JJlufl'; in qu;irtzite, north of Tempe Vale. 



