HOHN EXPEDITION PAL.5;oNTOLO(;Y. 109 



fine gruwtli-lint'S, p.irticularly on the pust-doryal area. Hinge-area narrow, with 

 tliree parallel, longitudinal, sliglitly arelied teeth posterior to the umbo ; anterior 

 teeth two, parallel. Dimensions of figured speeinien, wliieii is of small size : — 

 Anteroposterior diameter, 36 mm. ; uuibo-ventral diametei', 21 mm. ; greatest 

 dor.so-ventral width near to the posterior margin, 27 mm. A very large e.xample 

 measures 60 x 30 mm. 



Zoc. — In ijuartzite and sandstone, Tempo Downs, north of Tempo Vale, and 

 Finke (!orge. 



0/>s. — This species has some resemblance to the Ordovician species, P. biHiiigs- 

 iaiia, (Salter, and P. headi, Billings, in its area-like shape, but is distinguished by 

 its submai-ginal umljo and dilated post-dorsal area ; but it apparently exactly 

 resembles Modiolopsis iriiiicatus^ Ifall, from beds of corresponding in (Jhio and 

 New York, judging from the figure of that fossil on pi. ii., fig. 13, in Report Ck'ol. 

 Surv. Ohio, vol. ii., p. 86, 1875. 



Palaeai-ca tortuosa, sp. nov. (Plate Til., Fig. 31.) 



Sp. i/fiCz-.^Cast triangularly tiapezoi<lal in form, rapidly widening posteriorly; 

 axis oblique, corresponding with a high vaulted angulated ridge from the umbo to 

 the postero-basal angle, on each side of which the slope is precipitous, more so 

 dorsally than ventrally. Hinge-line straight, umbo at about the anterior one- 

 sixth ; hinge-area of moderate width, marked by two parallel and longitudinal 

 teeth, which extend for the whole length of the posterior side. Anterior side of 

 shell somewhat wing-like dorsally ; posterior margin nearly perpendicular to the 

 hinge-line. Surface of the cast marked by faint folds, which are slightly sigmoid 

 on the umbonal ridge. Length of hinge-line, 23 mm. ; of uml)onaI ridge, 26 mm. ; 

 of posterior margin, 16 nnn. 



Loc. — In quartzite. Mount Watt and between Petermann Creek and Teinj)e 

 Downs. 



Pteronites micans, sp. nov. (Plate I., Fig. 9.) 



Sp. char. — Shell transversely elongate, narrow lanceolate ; hinge-line sti'aight ; 

 beak small, nearly terminal ; anterior very short and narrowly triangular ; 

 posterior side truncate ; surface with six equidistant radial ridges. The cast of 

 the hinge-line presents a narrow parallel ridge terminating anteriorly at a small 

 pit, which may Ije interpreted to indicate a long cartilage furrow posterior to a 

 cardinal tooth. But for these characters the fossil might have been mistaken for 



