144 MR, C. A. MATLEY ON THE CAMBRIAN [Feb. 1902, 
projecting very slightly over the area, and pierced by a minute 
foramen (?). Internal casts show a short longitudinal groove 
at the umbo, towards the posterior end of which is a minute 
tubercle. The latter may be the cast of the pedicle-foramen. The 
“false area’ is traversed from apex to hinge-line by a pedicle- 
groove, and is crossed by the lines of growth. Two narrow 
muscular impressions diverge from near the apex of the valve, and 
terminate about half way towards the antero-lateral margins. 
Shell-substance tenuous, consisting of a few thin lamine, 
Surface of valves ornamented with very numerous, close, fine, con- 
centric lines of growth, which at intervals are strongly marked. 
In well-preserved examples the finer growth-lines are little more 
than ‘01 mm. apart. 
Two specimens measured in length 2 and 14 mm. respectively, 
and in width 2°5 and 1°5 mm. respectively. 
Horizon.—This is the characteristic brachiopod of the Lowest 
Black Shales. More than two dozen examples of the brachial valve 
and one dozen of the pedicle-valve were obtained by Prof. Groom 
from this horizon [M 257}. 
Observations.—Owing to the small elevation of the pedicle- 
valve, the reference to the genus dcrotreta is somewhat doubtful, 
but there is no question that it belongs to the family Acrotretide, 
Schuchert. In general aspect itis much hke Linnarssonia sagittalis, 
Salter, but its brachial valve is flatter and its internal characters 
are different. It is closely allied to Obolella (Acrotreta?) Sabrine, 
Callaway, of the Shineton Shales, and, I think, is only a variety of 
that shell occurring at a lower horizon. The variety has a longer 
hinge-line, the ornamentation is bolder, and the internal characters 
are rather different from those of the typical form. 
(Figs. 15 & 16.) 
The pedicle-valve of an undoubted species of Acrotreta appears on 
a tablet (LP 809) in the University Museum, Oxford, marked 
‘Upper Black Shales, Coal Hill’; 
Acrotrera sp. (cf. A. socialis, von Seebach). 
Figs. 15 & 16.—Acrotreta sp. 
cf. A. socialis, von Seebach. 
15. 18, 
a h 
a ae Sw) 
Sy > A LSS 
Fig. 15a = Internal cast of pedicle- 
valve; b= side-view; ¢ = view 
of the cardinal area. University 
Museum, Oxford. 
16 = Brachial valve, probably of 
this species. Worcester Museum. 
Fig. 
5 
Prot. Groom thinks that the 
specimen comes from a dark zone 
in the Grey Shales. It’is an 
internal cast, very minute, being 
not more than 1 mm. in length, 
and it shows the pedicle-groove 
plainly. There is a very similar 
valve from the Black Shales, 
Malvern, on a tablet in the 
Worcester Museum, and with it 
is a brachial valve of equal 
minuteness, which probably be- 
longs to the same species, though 
it would be difficult to separate it from the corresponding valve of 
Linnarssonia Belti (Dav.). 
The Malvern fossil has a general resemblance to Acrotreta 
