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I I 37 



TERTIARY FAUNA OF FLORIDA "^ 



right cardinal more prominent and stem-like, the left cardinal obsolete ; in 

 some specimens the resiliary insertion was directly on the surface of the valve, 

 in others (probably more mature) there was a distinct thickening, especially 

 about the margin of the scar. Lon. 2.2, alt. 1.7, diam. 0.6 mm. 



This shell is probably distinct from H. faba. It is more triangular, more 

 inequilateral, and more compressed. The sinuation of the base is much less 

 conspicuous, the cardinal tooth is longer, and the laminae proportionately shorter 

 that in H. faba. Several specimens with the valves in the natural position 

 indicate that there was a small external ligament in addition to the large 

 internal resilium. 



The hinge characters of both these species and the type H. arcuata seem 

 to me to be most nearly allied to those of M ontaciita, especially those Monta- 

 cuta * which, like M. ferriiginosa Mtg., have only the right cardinal and the 

 left anterior lamina well developed. To these in Hindsiella is added a more 

 or less developed external ligament, and if the peculiar form of the shell is 

 due, as has been suggested, to a commensal situs on the ventral segments of 

 Crustacea it is not improbable that the animal wants the broad external frills 

 of the mantle which have been observed in the free M ontacuta. 



Hindsiella nephritica n. sp. 

 Plate 45, Figure 8. 



Oligocene of the lower bed at Alum Bluff, Calhoun County, Florida ; Burns. 



Shell small, short, inflated, subequilateral, with rather prominent umbones, 

 near which the valves are smooth, elsewhere with irregular, more or less 

 prominent incremental lines; centrally vertically constricted, which produces 

 a shallow insinuation in the basal margin; umbones prosogyrate with the 

 dorsal margin impressed in front of them; hinge narrow, in the right valve 

 a single subumbonal short tooth, behind and below the beak a narrow elongate 

 scar for the resilium, and farther back a slender posterior lamella separated 

 by a groove from the dorsal margin ; adductor scars narrow, rather high up ; 

 interior of the shell polished with entire margins. Lon. 4.75, alt. 3.5, diam. 

 3 mm. 



A single right valve of this species was collected. 



* Other forms which, from their arcuate outline, have wrongly been referred to 

 Hindsiella will be discussed under Bornia, Pythinella, and M ontacuta. 



