92 SUPPLEMENT TO THE 



ever, they are more extended, and form a strong downward curve, tlie convex side of 

 which is towards the ventral valve. Laterally this process in Nucleospira and Athyris has 

 a very beak-like appearance — an appearance which is rendered all the more prominent by 

 the primary lamellae being widened (slightly in Nucleospira and still more in Athyris) 

 from the end of the hook-shaped processes to the point where the loop commences. The 

 primary lamellae, as they follow the curve of the bottom of the dorsal valve, converge to a 

 little less than half the length of the spiral, where they give forth short converging 

 lamellae, which are slightly or more strongly undulated in shape, and which proceed 

 straight across between the spirals to their ventral side before uniting in a sharp angular 

 point. This point is turned upwards more or less gently or abruptly almost immediately 

 behind the primary lamellae on the ventral side. The end of the loop which is thus 

 turned upwards varies in length in different specimens, never being very long, and some- 

 times being barely perceptible. The hook-shaped attachments of the primary lamellae to 

 the hinge-plate descend close to the pointed end of the loop, towards which they converge 

 on either side. The close proximity of the pointed end of the loop to the hook-shaped 

 attachments referred to often gives the appearance of an actual connection between them, 

 and has added not a little to the difficulty of investigation. The two primary lamellae, 

 after giving off the processes which form the loop, diverge again as they proceed towards 

 the front, and by a gentle curve form the first spiral coil. We are, therefore, now fully 

 acquainted with the interior and exterior characters of this important genus and species. 

 It occurs in immense numbers throughout the Wenlock Limestone and Shales. 



Nucleospira pisiformis, Hall, from the Niagara group of Waldron, Lidiana, and 

 Nucleospira ventricosa, Hall, from the shaley limestone of the Lower-Helderberg group, 

 Albany County, New York, cannot be specifically distinguished from Sowerby's Nucleo- 

 spira pisum. None of the many hundred specimens of N. pisum that have passed through 

 my hands exceeded five lines and a half in length by six in breadth and foui' in depth ; 

 only exceptional specimens attained these proportions. 



-Retzia, Kiny, 1850. 



4. Retzia Salteri, Z)r^y. Sil. Mon., PI. XII, figs. 21, 22; and Sil. Sup., PI. IV, 

 figs. 12, 13, 14. 



Nothing further relating to the type of the genus Retzia, viz., Betzia Adrieni, de 

 Verneuil, is known beyond the fact that the shell was provided with spiral appendages. 

 Mr. Charles Barrois kindly sent for my examination several examples of the fossil he had 

 collected at St. Arnao (Oviedo), Spain, but none of them, unfortunately, were workable. 



