82 



SUPPLEMExNT TO THE 



— NuCLEOSPlRIDiE, Bav., 1881. 



First Division 



The genera placed in this family seem, as far as our present knowledge of them 

 goes, to be nearly connected. 



J- Nucleospira, Hall, 1859; types Ter. jjisum, So\\. = A^. vetitricosa, 

 I Hall. 



Retzia, Kin(/, 1850 ; type T. Adrieni, de Verneuil. The connec- 

 tion of the spirals in this species are unfortunately not yet dis- 

 covered. King and myself therefore adopted R. Salteri as the 

 type, and its interior characters are now well known. Rhyncho- 

 sjoira, Hall, 1859, we consider to be a synonym of Retzia; his 

 type agrees with R. Salteri. 

 ^ Meristina, Hall, 1867 ; type T. didi/ma, Dalraan = M. niiida. Hall. 

 ? Treraatospira, Hall, 1857 ; type, S. multiplicata. Of this genus 

 all that has been discovered is that its spiral appendages are 

 directed towards the lateral margins of the valves. Nothing is 

 apparently known with respect to the connection of the principal 

 spiral coils, or of their attachment to the hinge -plate. The genus 

 , is consequently only provisionally recorded and placed in the 

 family Nucleospirida, from which it can be removed when the 

 connections shall have been ascertained. 

 Second Division — Dayia, i)ay., 1881 ; type T, navicula, Sow. 



Third Division — Uncites, Defrance, 1825; type U. gryphus, Defr. In 1849 



A. d'Orbigny proposed a family, Uncitides, for this species, but 



he knew nothing about its interior characters, as they had not 



been then discovered. 



In all these genera the extremities of the spiral cones are directed towards the lateral 



margins of the shell, and the connections of the principal stems of the spirals are simple 



and nearly similar. 



Nucleospira, Retzia, and Meristina present such small differences in their interior 

 arrangements that it will probably be desirable to include them all in a single genus. 

 In all of them the primary lamellae give off short lamellae, which proceed straight across 

 between the spirals to their ventral side before uniting in a sharp angular point. All of 

 them have their principal lamellae attached to the hinge-plate in a nearly similar manner, 

 a small difference being observed only in the case of Nucleospira, which has its attach- 

 ment more hook-shaped, as in Athyris plano-sulcata. 



Dayia differs considerably from the genera already alluded to ; but as the principal 

 stems of the spiral cones are connected in a somewhat similar manner to what we find in 



