70 BRITISH SILURIAN BRACHIOPODA. 
valve, and reaching to near the posterior margin ; external surface ornamented as in the 
opposite one. Interior unknown.  ‘T'wo specimens measured— 
Length 7, width 73 lines. 
» 16, 8-5. & 0 Sowerby s*type): 
Obs. Sowerby’s short description, “lenticular, punctated,”’ and his accompanying 
very imperfect figure, afford no idea of the species named Orbicula granulata in his 
description and O. punctata in the explanation of his figure. One of these names only 
can be retained, and, as that of “pwnctata” is best known, it has been adopted. In 1847 
Mr. D. Sharpe redescribed the same species under the designation of Zrematis punctata :-— 
“Ovate, depressed, surface smooth, punctations very large. Length 3ths, breadth 3 inch. 
Found in the Caradoc sandstone at Chatwall, on the east flank of the Caradoc. The 
specimen described by Mr. Sowerby [an internal cast] is now in the Geological Society’s 
collection ; it is very imperfect, and does not show the principal characters of the species. 
Mr. Sowerby placed it in Ordicula with a mark of doubt.” However, neither Sowerby nor 
Mr. Sharpe seems to have understood the character of the shell they had the intention of 
describing, for they mistook the pits formed by the little hexagonal network for punctures, 
while, as stated by Dr. Carpenter at p. 39 of my ‘ General Introduction,’ “The shell does 
not depart in any essential particular from the type of Discinide, the supposed punctated 
surface being (as in Poraméonites) a mere superficial conformation, and Mr. Sharpe’s 
‘internal unpunctated layer’ being a succession of lamine, such as in Discina.”’ At p.68 
of Mr. Sharpe’s above-named paper he describes his genus Zrematis as “a sub-orbicular, 
inequivalve Brachiopod, attached by a ligament passing through a longitudinal fissure in 
the posterior part of the ventral valve. Valves united by a hinge, which is supposed to 
resemble that of Zeredratula, and is accompanied in the dorsal valve by three diverging - 
internal plates. Shell regularly punctated externally, nearly fibrous, and_ slightly 
striated internally.” 
This description is evidently founded partly on suppositions and erroneous observa- 
tions. Mr. Sharpe swpposes only that the valves are united by a hinge resembling that 
of Terebratula ; but his specimens and his figures show no evidence of such having been 
the case; nor does Prof. J. Hall, in his description of Ordbccula terminalis (the type of 
Sharpe’s genus Zrematis), make any allusion to an articulated hinge as in Zerebratula ; 
and all analogies tend to make us believe that its valves were, as in Discina, kept im place 
by muscular action, and not through the medium of teeth and sockets, as in Terebratula. 
Indeed, since we are not in possession of the internal surface of the valves of any of the 
known species of Zrematis, we cannot point out any differences which might entitle 
Mr. Sharpe’s so-termed genus to be distinguished from Descina proper. ‘The cell-like 
or net-like sculpture is not quite regular over the surface in all specimens ; for at times, after 
a sudden interruption in the growth of the shell, the cells began again, by being smaller or 
larger than those which existed at the time the interruption took place. Up to the 
present time D. punctata had not been properly figured. I have therefore endeavoured, in 
