43 
The genus Accinthothyris appears in the lower beds of the 
Inferior Oolite, and extends up to the Middle Oolites; it has 
not yet been found in the Cretaceous or Tertiary strata, but a 
living spinose Rhynchonella ( Rhynchonella Doderleini ), has been 
described by the late Thomas Davidson, and published after 
his death. (Annals. Natural History, January, 1886.) 
The Jurassic Rhynchonella) can readily be divided into several 
groups which are found to carry on, as they ascend, each their 
own course of development side by side. Roughly speaking, 
these groups are as follows :—■ 
(1) The Lncunoso- group. 
(2) The Tetrahedra-gi'oii]). 
(3) The Concinna-giowp. 
(4) The Varians-gron-p. 
(5) The Obsokta-gvowp. 
(6) The Acuta-growg. 
(7) The Ri/nosa-gvoiig. 
(8) The Sjjinosa-gYou p. 
The relations of these groups to each other, and the division 
of the genus Rhynchonella into genera or sub-genera, we 
propose to discuss in a future paper. 
Part II. 
The Spinosa-gioiig (Genus Accinthothyris cl’Orb) with which 
we are only concerned in this paper, is distinguished from all 
others by the presence of spines upon the valves. 
The type species of this group is Acanthothyris spinosa , 
of which the following is the history, along with that of 
Acanthothyris senticosa. It is necessary to consider these 
species together to avoid repetition. 
A spinose Rhynchonella was figured by Knorr and Walch 
(Lapides Diluvii Testes, French translation (Description des 
Cocjuilles et Autres Corps Petrifies, 1768, Yol.n., Section 1., Plate 
B iv., figure 4.) The figure is very good, and represents a 
large-sized Rhynchonella spinosa. At page 77 they give the 
following description of the figure, N 4.—“Monsr. Prof, le 
d’AxNOME nous donne la description suivante de cette coquille: 
C’est la Petrifaction d’une Concha anomia ventricosa , striata 
echinata , je ne la trouve pas dans Linnaeus, & je le nomme 
