164 PERMIAN FOSSILS. 
establishing of the genus Hdmondia by De Koninck renders it necessary for me to 
modify A//orisma by restricting it to the kind represented by Hiatella sulcata, Another 
opportunity will herein occur to speak more in detail of the latter genus. 
There is much difficulty in distinguishing the various species of Hdmondia, in con- 
sequence of their resembling forms belonging to other genera, and rarely displaying the 
essential characters of the genus. Thus the generic collocation of the so-called Sangu- 
nolaria undata, Portlock, is far from being correctly determined. Iam inclined to think, 
if this species is not an Hdmondia, that it belongs to a genus closely related to it; as 
there is some appearance of a deep vertical cartilage-plate (though much reduced in size, 
compared with that of Hdmondia sulcata, Ld. unioniformis, and other species), occupying 
about one third of the length of the dorsal margin of the valves: perhaps it belongs 
to the genus Orthonota of Conrad, which is typified by a similarly-formed shell, the 
Orthonota undulata, Conrad, characteristic of the Hamilton group of rocks (Devonian) 
in North America. 
Synonymous with Hdmondia is Professor M‘Coy’s Sanguinolites,’ which is typified 
with Phillips's Sangwinolaria (2?) angustata, a species having (as well as the one 
[ Sanguinolaria arcuata, Phillips] next in order of description in the ‘Synopsis of the 
Carboniferous Fossils of Ireland’)’ all the characters of the present genus.* 
Hdmondia appears to be a smgular genus, both in its cartilage fulcra and muscular 
system. The former, as existing in Hdmondia sulcata (Sanguinolaria id., Phillips), are 
represented in Plate XX, figs. 2a, 3, and 4. By referring to these figures, it will be 
seen that the plates are situated within the umbonal cavity, and have a striking re- 
semblance to a bivalve shell. ‘The figures cited are copies of a fossil (cast) which was’ 
originally in the state represented in figure 1; but by, carefully chipping off the 
umbones, it was made to display two plates, singly curving with each of the 
umbonal cavities, as in figure 2a: both occupy their exact relative position in (the 
magnified) figure 4; and figure 3 is an enlarged representation of the most perfect one. 
Having broken off the umbones of a number of specimens with the like result, I can 
speak with confidence as to these plates belonging to the shell; and I am equally 
confident, from what is displayed in several sections which I have made of the shell 
from the dorsal to the ventral margin, that each one is attached by its upper margin 
to the hinge-plate in both valves. Looking at such shells as Lutraria elliptica, we 
discover that similar structures serve as supports or fulcra for the cartilage: we are 
therefore led to conclude that the plates of the fossil under consideration have ~ 
1 Vide Synopsis of the Carboniferous Fossils of Ireland, p. 47. 
2 A specimen of Sanguinolaria (?) angustata in the Gilbertsonian collection of the British Museum, 
exhibits the groove left by one of the cartilage fulera: casts of Sanguinolaria arcuata, with the grooves left 
by the cartilage fulcra, are rather common at Redesdale in Northumberland. 
3 Professor M‘Coy has included species of various genera in his Sanguinolites: some appear to be 
Allorismas (e. g., Sanguinolaria tumida, Phillips) ; and others Pleurophoruses (Sang. tricostata, Portlock) : 
S. undatus is perhaps an Orthonota; 8. contortus appears to belong to an undescribed genus; and S. 
radiatus 1s seemingly a Janeia. 
