Palceozoic Fossils. 373 



furrows between, the mesial furrow with a slight fokl down the 

 centre, and continued uninterruptedly up into the castof the beak. 

 Hinge area straight or curved forwards, with numerous fine longi- 

 tudinal striae and the cast of the beak rising to it in the same 

 plane as the surface of the cast of the shell. Furrows sometimes 

 show on the sides of the cast of the beak, at other times this latter 

 is quite smooth, the difference being due either to the original 

 thickness of the shell, or to its having been subjected to solution 

 before being imbedded. In the dorsal valve the median fold has 

 the same furrow as in Sj/. orbignyi ; the sinus in the ventral valve 

 has a slight median fold. The shells are usuallj- distorted, r<^nder- 

 ing one end of the alae very pointed, while the other is markedly 

 rounded. The hinge area is usually vertical, but one vej-y rarely 

 finds the actual shell undisturbed. In Sharpe's figures one is look- 

 ing at the impi*ession of the hinge area surface ; in the specimen I 

 figure the beak in the pedicle (Sharpe says dorsal) valve is very 

 strongly curved over, and the hinge area likewise curved, as in 

 von Buch's figure of Sjj. capetisis. It is this fact that makes me 

 think that von Buch's species was founded on specimens of Sjj. 

 antarcticus and not of Sp. orhignyi, though tlie other features 

 seem to agree more nearly with the latter form. The diff^erent 

 ways in which the shells have been jjreserved, sometimes imbedded 

 with the two valves adherent when the internal cast is complete, 

 at others with the inteinal casts of the dorsal and venti-al valves 

 separately fossilized, make it extremely ditficult to fix on specific 

 characters, and i think it the safest to have only one species for 

 the commoner forms. 



Ulrich's S/jn'/cf chiiqiiisdca seems closelj' allied to Sp. (ttiforc- 

 ticus, Imt I do not think with Kayser and Reed that the resem- 

 blances are sufficient to identify the Cape specimens with those 

 from Bolivia. Sp. huarquianus, Katzer, is guit^ distinct from 

 Sp. antarcticus., while Sp. coflhanas, Katzer, stands very near. Reed 

 separates the very broad ribbed form which Sharpe figures (PI. 

 XXVI, fig. G.) as Sp. vogeli, v. Ammon, and as it is closely allied 

 to Sj). antarcticus, and this latter possesses the surface ornamenta- 

 tion which von Ammon figures, the species will stand ; I have 

 never seen the form. With regard to the form which Reed refers 



