BOTANY AND ZOOLOGY. 
93 
culated, warty, or even cylindrically or ramosely elevated. Through 
weathering and attrition, the summits of these eminences became worn 
down through one or more of the layers, so as to exhibit concentric 
rings. The summits and their vicinity acquire chinks or fissures, as 
the learned author expresses it, which penetrate the first beds of the 
net-work, and thus form vermicularly diverging furrows. The apex of 
the tubercle is frequently perforated by a hole, which, in some in¬ 
stances, is considerably enlarged and surrounded by one or more series 
of smaller holes. 
This organism, in its various states of growth and weathering, pre¬ 
sents the varied forms which the author had previously described as 
Tragos capitatum , and Geriopora verrucosa , — in some instances, also, 
bringing out the characters of Mermecium and Siphonia ,—facts which 
lead him to conclude with the just reflection that in the classification 
of organic bodies we must be guided by the essential organic structure ; 
for mere surface physiognomy is capable, as in this case, of leading to 
the admission of several genera within the limits of even a single 
species. 
In 1839 Lonsdale, besides characterizing a new species (S. nummu - 
, having a flattened, discoidal form, from the Wenlock lime¬ 
stone, identified S. concentrica , from the Wenlock limestone and shale 
(Silurian System, pp. 680-1, pi. xv., figs. 31 and 32). The latter 
was properly made a new species by D’Orbigny in 1847, under the 
name of S. striatella , in consequence of the much greater compression 
of its layers (Prodrome de Pal. I., p. 51) ; and this change was adopted 
by McCoy in 1851 and by Murchison in 1859 (Siluria, p. 210). It 
is a maspive coral, like S. concentrica , and is generally represented as 
growing around some submarine organic body. 
In 1847 Prof. Hall characterized the genus Stromatocerium to re¬ 
ceive an obscure species from the Black River limestone, which he 
named S. rugosum (Pal. N. Y., I. p. 48, pi. xii., fig. 2). Judging 
from the description and figures, this fossil is completely congeneric 
with Stromatopora concentrica , and has been so regarded by D’Or¬ 
bigny, Pictet, Billings, and others. 
In the same year, D’Orbigny separated the tuberculated and mam- 
millated forms of S. polymorpha as constituted by Goldfuss, and 
established for their reception the new genus Sparsispongia with the 
species S. polymorpha , radiosa , and ramosa (Prod, de Pal. I., p. 109). 
