Pcdcpozoic Bivalved Entomostraca . 31 



1. Carbonia fahulina^ Jones and Kirkby. 

 (PI. II. figs. 1-10.) 



Cythere fahulina, J. & K. Trans. Geol. Soc. Glasgow, 1867, vol. ii. 



"p. 217. 

 Cythere ? fahulina, J. & K. Geol. Mag. 1870, vol. vii. p. 218. 



i. Typical examples', length -^ -J^, and -^ inch. 



More or less bean-shaped. Dorsal border arched, highest 

 behind ; anterior extremity more acutely rounded than the 

 posterior ; ventral border straight or slightly incurved about 

 the middle, where the right valve overlaps the left. Height 

 more than half the length, sometimes fully two thirds. Dor- 

 sal and ventral aspects acutely ovate, widest behind. Surface 

 of most specimens smooth, but, in well-preserved valves, 

 pitted or rudely reticulate. A circular muscle-spot, subcen- 

 trally placed, is indicated externally in some examples ; but it 

 is best seen in casts as a slightly raised spot or tubercle. 



The above gives the characters of what may be taken as 

 typical examples of the species. Other specimens show dif- 

 ferences that appear of varietal value. The more important 

 of these are : — 



2. Var. humilis. (PL II. figs. 11-14.) 



Elongate; dorsal border flatly convex; extremities rounded 

 and more nearly alike than in type specimens; ventral border 

 straight. Length -^ to -^ inch. 



3. Var. inflata. (PI. II. figs. 15-19.) 



A thick-shelled, obese form, greater in width than in height, 

 and with the greatest width nearer the posterior end than in 

 other forms, which thus gives the dorsal and ventral aspects 

 of the carapace a subcuneiform outline. Length -±y inch. 



4. Var. suhangulata. (PI. II. figs. 20-23, and 24?.) 



A gibbous, robust variety, of great relative height, with a 

 subangular dorsal border, and a very abrupt postero-dorsal 

 slope. Length T ! T inch. 



This variety is the largest of any of the forms of G. fahu- 

 lina. We figure with it a specimen from Millburn, Campsie, 

 which possesses a similar dorsal border, but less angulate, 

 and of very different relative height (fig. 24). This may ulti- 

 mately prove to belong to another variety. 



C. fahulina has some resemblance to Cythere cuneola, J. & 



