104 
PALEONTOLOGY OF NEW YORK. 
Many of the species originally included under this designation have been re¬ 
moved by the establishment of such generic divisions as Rhynchospira, Trema- 
TOSPIRA, Eumetria ; but, as the determination of generic values in all these 
fossils is usually attended with difficulties, it is highly probable, and indeed cer¬ 
tain that there are several distinct types of generic structure represented among 
the commoner species referred to Retzia. It will be necessary to determine 
the value of this genus from the characters of the species Terebratula Adrieni, 
designated by Professor King as its type; and our observations upon it lead 
to the belief that, strictly regarded, it presents a type of structure of rare 
occurrence, and with present knowledge no other species can be placed in the 
same association. 
Terebratula Adrieni was described by de Verneuil in 1845* from the lower 
Devonian of Spain, but our fuller knowledge of the species is due to the de¬ 
scriptions and figures given by Dr. (Ehlert, who has identified it from the 
lower Devonian of the Departement de la Sarthe, Sable, Brulon, etc., 
France, f 
With the help of Dr. QEhlert’s published work and with his most consider¬ 
ate personal assistance, :|: we have made an earnest endeavor to develop the 
structure of the brachidium in this species. Unfortunately the specimens 
accessible were filled with a hard, opaque calcareous material, and such details 
as have been made out were obtained by the process of serial transverse section¬ 
ing. The nature of the interior of the brachial valve and the structure of the 
hinge-plate had already been demonstrated by OEhlert, and the results obtained 
in regard to the structure of the loop are so peculiar as to require corroboration, 
which the material at hand does not permit. The following account of the 
characters of the species represents the sum of our present knowledge of the 
genus. 
* Bulletin de la Soci6te geol. de Prance. 2d Ser., tom. 11, p. 471, pi. xiv, figs. 10, a-d. 
t See QUhlbrt ; Etudes sur quelques Fossiles devoniens de I’Ouest de France; Annales Sci. Gdol., 
t. xix. No. 1, p. 24, pi. xi, figs. 11-19. 1886. 
t Appreciating the necessity of making a thorough study of this rare species, we twice applied to Ui-. 
OEulbrt for specimens, and he has most generously met these requests, not only with a number of examples 
fi-om the Departement de la Sarthe, but with copies of unpublished sketches of sections. This generosity 
and spirit of helpfulness is most coi-dially acknowledged. 
