75 
is also the only one that is quite straight ; the lateral folds, nuail)ering about 
seven on each side are more or less arched according to the position they 
occupy, and the thickness diminishes in proportion to their distance from 
the mesial fold. The dorsal valve is almost as deep as the opposite one, 
and slightly sinuated in the median portion ; it has the same ornamentation 
as the last-mentioned, and the anterior margin is a little prolonged, so as to 
make the marorin at the front sinuous. 
O 
Dimensions. — Length, six millimetres ; width, seven millimetres ; 
thickness, five millimetres. 
Delations and Differences. — This species is distinguished from all 
Devonian congeners, hy its small size, and the shape and number of its folds. 
Horizon and Locality. — A single specimen rather well preserved on 
account of the shell being silicified has been found in a compact black lime- 
stone from the Yass District. It is associated with a fragment of a Spirifer 
related to Spirifer Paillettei, de Verneuil. 
Genus — DH YNOHONELLA, Fisher de JFaldheinn. 
1. Ehynchonella pleurodon, Fhillips. 
Terehratula pleiirodon, J. Phillips, 183G, Geol. Yorkshire, II, p. 222, pi. 12, fig. 25-30 
(fig. IG, excl.) 
35 5 5 Idem, 1841, Pal. Poss. Cornwall, &c., p. 8G, pi. 35, fig. 155. 
Airy pa multidens, A. d’Orbiguy, 1S50, Prodr. Pah, I, p. 94. 
Rliynchonella pleurodon, . 1 . Morris, 1854, Cat. Brit. Boss., p. 147. 
33 3 3 T. Davidson, 1865, Mon. Brit. Dev. Brach., p. 62, pi. 13, 
figs. 12, 13. 
33 {Stenocisma) Tethys ? J. Hall, 1867, Pal. N. York, IV, p. 335, pi. 54, 
fig. 1-8. 
5 3 3 3 Sap2AiO ? Idem, 1867, ihid., p. 340, pi. 54. fig. 33-43. 
53 3 3 dotis ? Idem, 1867, Pal. N. York, lA^ p. 344, pi. 54, fig. 11-20. 
35 pleurodon. L. G. de Koninck, 1873, Becherches Aniin. Boss., II, p. 50, 
pi. 2, fig. 15. 
Shell of medium size, usually transverse, oval in shape, valves more or 
less gibbous, with a rather variable number of radiating angular folds, havinc^ 
their origin at the beaks ; these folds are separated from one another through 
a great part of their extent hy rather deep furrows, of which the bottom is 
also angular ; the mesial folds are almost straight, while the lateral are more 
M 
