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SUPPLEMENT TO THE BRITISH 
ribs, commencing at about one third of the length of the valve ; beak small, angular. 
Dimensions (of the largest specimen I have seen) — 
Length 6, width Q^, depth 3 lines. 
Obs. — This small species is remarkable on account of its trigonal shape, three short 
sub-marginal ribs, and smooth lateral portions of the valves. Mr. J. Thomson, who 
discovered the shell, observes to me that it is unlike Mh. pitgnus and Bh. pleurodon. It 
approaches most in shape to some small individuals of Rh. mesogonia, Phillips, but is less 
transverse. It somewhat resembles some examples of Camaro'plioria glohidina^ but does 
not belong to tliat genus. It occurs in Carboniferous shale at Brockley, Lesmahago, 
Lanarkshire. 
Sub-genus Rhynci-iopora, King. 
Type species Rhyncliopora Geimtziana {Tei-ehratida, Verneuil). Geol. Russia, vol. ii, p. 83, 1845. 
"Diagnosis — Rhynchonelliform. Shell-structure perforated, the perforations passing 
through from one surface to the other in both valves. 
" Obs. — As will be seen, this genus (or it may be sub-genus) differs from Bhgn- 
chonella simply in having the shell-substance of its valves perforated similarly to what 
prevails in Spiriferina, Terebratula, and other Palliobranchs. Its internal structure 
appears to be the same as that which characterises the type genus Mh.ynclionella ; two 
diverging dental plates are present in the large valve ; it is possible, however, that when 
the valvular cavity is fully made known, the apophysary system of the small valve may 
be a modification in the type genus. In form THiynchopora closely resembles BhgnchoneUa. 
Two species only known as yet ; one belonging to the Carboniferous and the other to the 
Permian system." (King, MS.) 
20. Rhynchopora Yotjngii, Dav. Sup., PI. XXXIII, figs. 11, l\a,b,c. 
EiiYNCHOPORA YouNGii, Bav.. MS. Young, North British Daily Mail, December 3rd, 
1878. 
Shell small, somewhat tumid, nearly as long as wide. Yalves almost equally deep, 
with about seven short ribs in each valve, extending only to a short distance from the 
front and lateral margins ; umbonal region smooth. Median fold in dorsal valve of 
moderate elevation, with three short, stout ribs. Sinus in opposite valve with two short 
ribs, split longitudinally to some short distance from the front ; beak small, much 
