350 GEOLOGY AND PETROLOGY OF THE GREAT SERPENTISE BELT OF X.S.W., 



Spirifera STRIATA (Sowerbv). (Plate xx.. figs. 1-3.) 



Sowerby, Min Coneli., 1820, t. 270; Daviason, Brit. Caib. Bracii., 1852, p. 19, t. 2, 

 f. 12, 14: t. 3, f. 2-6: Ibid. Carb. Suppl.. 1880. p. 274. t. 31. f. 1. 2, 3, 4; 

 Dun, Kec. Geol. Sun.. X.S.W.. vii.. Ft. 2. 1902. p. 8.^-4. t. xxii.. f. 6-9. 

 and Bibliogxaphy. 



As may be seen from Davidson's figures, there is considerable variety in tUe 

 forms grouped under this species. Three specimens are illustrated here. That 

 represented by Plate xx., lig. 1, closely resembles Davidson's illustration (op. cit. 

 ■iupra, t. 3, f. 4), though the ribs are not so numerous. It is the most alate of 

 the three. There are about fifty radial ridges ei-ossed by faint concentric lines. 

 The sinus of the pedicle valve is somewhat deeply impressed near the margin, 

 which is here flexed rather sharply and projected like a tongue in the dorsal direc- 

 tion. The beak is not quite centrally placed in one form. Its dimensions are 

 (restored) : Breadth. 55 mm. : length, 23 mm. The other forms are less broad. 

 That shown in Plate xx., fig. 3, has forty strongly-marked ribs, on wliich slight 

 beading gives the only traces of concentric ornamentation. The (restored) 

 breadth is 36 mm., the lengih 25, and thickness 14 mm. That shown in Plate xx., 

 Sg. 2 has less accentuated ribbing with scarcely any other ornamentation. There 

 are about fifty ribs which are much narrower and more closely spaced towards the 

 ears than in the median portion of the shell. Brcadtli (restored). 56 mm.; length, 

 30 mm. ; thickness, 18 mm. These three forms were collected by Mrs. Scott from 

 the south-east of Babbinboon. They were also obtained by Mr. Pittniau in 1897 

 from the "Whale's Egg,'' 5 miles S.E. of Somerton. 



This form appears to occur throughout the Carboniferous limestone, and is 

 most characteristic of its lower portion (Davidson, op. cit. sup. p. 21). The re- 

 cent workers record the range of the form in the British Isles as from the zone 

 of Ci to that of Di. 



Spirifera steiato-cox\'Oluta. sp. nov. (Plate xx.. figs. 7, 8.) 



This form is intermediate in character between ,S'. striata (Sowerby) and <S. 

 convoluta (Phillips). It is broader in proportion to the length than 5. striata 

 but not so broad as convoluta. The hinge line resembles that of convoluta in ex- 

 tending the fnll width of the shell. The area also is narrow, with parallel sides, 

 is marked by faint transverse striation, and jiierced by a triangular delthyrium. 

 The ribs, both simple and intercalated, are about sixty in number, and arc almost 

 as numerous as in the larger forms of iS. striata, and more so fiuin is normal for 

 S. convoluta, though Davidson illustrates a form of S. convoluta (Biit. Carb. 

 Brach., t. 5, f. 9-10) in which the broad mesial ribs are succeeded (but on one side 

 only) by numerous narrower ribs, there being altogether twenty-seven ribs on this 

 side of the shell as against twenty on the other side. Our form is more sym- 

 metrical and the ribs decrease gradually in size from the mesial portion to the ears 

 of the shell. Tlie rather sinuous character of the ribs acconls with S. convoluta 

 rather than S. striata, though it is not unknown in the latter. There i.s little sign 

 of a concentric ornamentation, for the form is partly decorticated, but the growth 

 lines give an appearance of overlapping lamellae. The valves are approximately 

 of equal convexitv the shallow sinus on the pedicle valve corresponding to a 

 mesial fold on the dorsal which becomes more elevated near the margin, and is 

 bent backwards into a tongue-like projection. No internal structures are visible. 

 Dimensions: Length. 25 mm.; breadth. 49 mm.: thickness, 9 mm. Coliccted by 



