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TERTIARY FAUNA OF FLORIDA '^ ^ '^ 



virente," and the number of teeth he ascribes to it, I feel compelled to believe 

 that it could not have been Y. glacialis, whatever Gray's N. arctica was.* 



Sections : 



A. Yoldia s. s. Type Y. hyperborca (I.oven MS.) Torell. 



Shell elongate, smooth, compressed, more or less pointed behind, 

 having a deep pallial sinus and with a wide pedal and moderate si- 

 phonal gape. Ex. Y. Icevis Say, Miocene, Virginia. 



B. Cncstcriiiiii Dall. Type ]' arctica Brod. and Sby., Zool. Journ., 1829; 



(not of Gray, Parry's Voy. App., 1824) =^ Y. scissurata Dall. 



Shell like Yoldia with incised sculpture not in harmony with the incre- 

 mental lines over more or less of the external surface. Ex. Y. laiicco- 

 lata J. Sby., Pliocene. 



0. Orthoyoldia Verrill. Type Y. scapina Dall. 



Shell smooth, without rostrum or carina, the ends bluntly rounded. 

 Eocene, recent. 



D. Yoldiclla Verrill. Type Y. Iticida Loven. 



Shell small, rounded ovate, smooth, with obscure rostration feebly 

 developed, with a small or indistinct pallial sinus ; resilium well devel- 

 oped, short, sometimes partly visible externally. 

 These are mostly small deep-sea forms, of rather generalized character, 

 which verge on Mallctia in their ligamental features, and are very much like 

 the young of some of the larger forms. Professor Verrill ascribes to them 

 a feeble external ligament, but it seems to me more like the continuous peri- 

 ostracum which is visible in a fresh specimen of Y. ihracicsforinis, and which 

 has no real ligamentary function. The dorsal valve margins do not entirely 

 close over the resilium, though its attachments appear to be wholly internal. 



E. Portiandia Morch. Type Y. glacialis Wood (+ Y. portlandica Hitchcock, 



Pleistocene and recent. Mcgayoldia Verrill). 



Shell convex, more or less abruptly truncate behind, the rostral part 

 laterally compressed ; the pallial line with a deep sinus. 



The gaping of the valves in Y. thracicefonnis is merely a specific character 

 and varies in the same species and in different ages of the same individual. 



* In this also I agree with Hanley and Smith in referring Gray's species to the hyperborea group 

 rather than to that of tnaicata Brown, as supposed by Torell, Jeffreys, and Morch. Yoldia arctica 

 Brod. and Sby. (1829) is a tota.lly distinct species, which I have named K scissurata. 



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