79 
sinus occupied by tliree adjacent ril)s, of Avliicli the two lateral are a little 
less prominent than the middle one. The surface is covered with ribs similar 
to those of the dorsal valve, twelve or fourteen in number. 
The beak, as far as it has been possil)le for me to free it from the 
matrix, appeared small. Tlie margins of the two valves show at the front a 
well-marked sinuosity. 
Dimensions . — -Lengtb, twelve millimetres ; width, nine millimetres ; 
thickness, four millimetres. 
Delations and Differences.-— This species has inuch resemblance to 
Atrypa promimda, Iloemer, of which it has almost the same outline ; it differs 
from it in its small size, in the less convex form of the valves, in the greater 
sinuosity of the frontal line, and in the number of ribs which in the maximum 
is but fourteen, while in the species from the Eifel it is twenty. It differs 
from A. Adrienni, de Verneuil, in the more elongate form and small number 
of ribs as well as in the sinuosity of the frontal line. 
Horizon and Locality. — A very small number of individuals of this 
species has been collected in a black limestone from the Yass District. 
Genus — SPIRIDEll, Soicerhy. 
1. Spikifer DIS.JUNCTUS, Sowerhy.^ 
Spirffra disjuncla , SoAverby, ISiO, Trans. Geol. Soc. London, V (2), pi. 5.3, fig. S, and 
pi. 5L figs. 12, 13. 
,, calcarata, Idem, 1840, ibid., pi. 55, fig. 7. 
,, extensa, Idem, 1840, ibid., pi. 54, fig. 11. 
” (jigantea. Idem, 1840, ibid., pi. 55, fig. 1-4. 
Spirifer Verneulil, Murchison, 1810, Bull. Soc. Geol. France, IX (1), p. 252, pi. 2, fig. 3. 
„ Ar cilia Ci, Idem, 1810, ibid., pi. 2, fig. 4. 
,, Lonsdalii, Idem, 1810, ibid., pi. 2, fig. 2. 
Spirifera, d isj uncta , .1. Phillips, 1841, Pal. Foss. Cornwall, etc., p. 71, pi. 20, fig. 128, yj y, li ; 
fig. 129, and pi. 30, fig. 120. 
,, protensa, Idem, 1S41, ibid., p. GO, pi. 28, fig. 118. 
^ ^ [Vide, E. Etheridge, Jiinr., Jourii. P, Soc. N. S. Wales for 1S80 [1881], XIV^, [). 255, pi., tig. 5.— 
SpirifcTA fliffuncta, — W, S. D. ] 
