BRACHIOPODA. 
11 
though losing none of its external characters. We may cite the apparent out¬ 
come of Spiriferina from the septate lamellose Spirifers; and Syringothyris as 
the final product of changes along the line of those plicate Spirifers with smooth 
fold and sinus. Such changes, then, which we recognize as having induced 
actual generic differences are confined to the interior and the intimate structure 
of the valves; external variations, as far as now known, when unaccompanied 
by internal changes, must be regarded as of altogether subordinate value. 
These external differences, however, make an excellent basis for a grouping 
of the members of this protean genus, and one not merely conventional and 
arbitrary, since it serves to indicate, within the integrity of the genus, lines of 
progress leading to resultants which are no longer congeneric. 
Several authors have proposed a classification of the Spirifers on the basis of 
their external ornamentation, and earlier writers were especially fond of 
attempts in this direction. Frequently the proposed arrangements have been 
vitiated by the inclusion within this genus of distinctly heterogeneous species. 
Thus with VON Buch’s classification in 1836 and 1837,* and to some extent 
with that given by Phillips in 1836.f The latter writer proposed six subdivi¬ 
sions of his Spirifers; a. Cuspidate; h, Angustata; c. Radiate; d, GlabratcE; 
e, Terehratuliformes; f, Filosa. The list of species referred to the last two divi¬ 
sions contained no Spirifers, but Athyris (e) and Schizophoria, Orthothetes 
and Chonetes (f). The Cuspidate were typified by S. cuspidatus, and this group 
is equivalent, in a restricted sense, to the genus Syringothyris, though it was 
also made to include species of Cyrtia, Derbya and Orthothetes. The Angus- 
tatce, and Radiatce, were separated on the basis of the length of the hinge, which, 
in the former, equaled or exceeded the width of the shell. Both included 
species with smooth and plaited fold and sinus. The Glohrata included both 
Spirifer glo.ber and S lineatus, that is, both Martini a and Beticularia. 
De VerneuilI divided the Spirifers as follows: I. .Anomcwa:, including the 
equirostres (= Porambonites) and bifores (= Platystrophia) ; II. Lisses, equiva¬ 
lent to Reticularia and Martinia, but embracing a species of Triplegia ; III. 
* Ueber das Genus Delthyris ; and Ueber Delthyris, oder Spirifer und Oi-this. 
t Illustrations of the Geology of Yorkshire, 
t Geologie de la Russie de I’Europe, p. 127. 1845, 
