nORN EXPEDITION — PAL/EONTOLOGY. 105 



(2.) A socond species is represented l)y iiitei-iial easts and flie inipiession of 

 tlie spire ; a restoration indicates a shell of tlu^ size an<l i;cneral outline of 

 Eiioiiiphalus pcntago>ialis, hut witli a flat inornate spire. Tt has occurred in sand- 

 stone at Chandler llange, and in quartzite between Peteriiiann Creek and Tempe 

 Downs, nortli side of George Gill Range and at Finke Gorge. 



(3.) A third species resembles C/////tVrt' ^^/7e'«' on a large scale; but the .spire 

 is more elevated, the uppei- surface of the whorls ilat, and the flange-like keel 

 imbricates over the suture. Only the impressions of the upper surface in quartzite 

 were obtained, though common, at Middle Valley (Tempe Downs), and at north of 

 Tempe Vale. 



(4.) A larger shell of the last type is indicated by a similai- impi'ession from 

 twenty miles west of Toko Waterhole in Cairns llange, on the Queensland 

 border ; it diflers in having spiral ridges in addition to the sigmoid growth-folds of 

 the last species. 



Class Lamellibranciiiata. 



Genus Isoarca, Minister, 1812. 



{Telliiiomya, Hall, 1847. Cfenodonfa, Salter, 1852.) 



The distinction of C/e/iodo/i/ii ( = Tclliitoniya) from Isoarca, whit'h was pro- 

 pounded by Salter, viz., that the former had simple cuived umljones and the 

 latter subspiral ones, is no longiu' tenable, as one species of the Larapintine rocks 

 has the umbones more markedly spiral than any described species of hoana 

 {sensu stricto), and therefore I adopt Woodward's opinion tiiat Ctoiodonta is 

 synonymic with Isoarca. 



I cannot formulate any set of characters, based on shape, direction of hinge, 

 disposition and form of teeth, by which the Mesozoic and Pahcozoic s))ecies may- 

 be kept in ditlerent genera ; indeed, if such a course were followed, it would be 

 necessary to establish several genera for the Larapintine species alone. Tlui 

 phrase " Nucula or Leda-like shells" has not a uni\crsal application, as maybe 

 judged from the various .species herein illustrated, not one of which resembles 

 either Nucida or Leda ; but associated with the dentition of Isoiurn there is I'cpre- 

 sented the form of Pt'ctHucuIiis, Ana^ Opis, Crassa/e/Id, Modio/a, etc. ; whilst an 

 extreme divergence tf) an orbicular outline is presented by /. orhiiuUiris. 



Isoarca etheridgei, sp. nov. (Plate IT., Fig. 15). 



Cteiiodouta, sp., Kthcridge, I'., \i., p. 2 1, t. ?>, ligs. G-S. 



