82 
Dimensions. — Width, thirty-five millimetres ; length, about fifteen 
millimetres ; thickness, twelve to fourteen millimetres. 
llelaiions and Differences. — In its general form this species resembles 
certain varieties of Sp. disjunctiis, Sowerby ; hut it is distinguished from it 
rather easily by the relatively lesser thickness in proj)ortion to the width ; in 
the smaller number of the radiating folds and the greater depth of the 
furrows that separate them from one another, and above all by the very 
marked difference of structure that may he seen in the two lateral folds of the 
mesial fold and consequently also of the sinus, when they are compared with 
the folds that ornament the rest of the surface. In Spirifer disjmictus this 
last character is almost entirely wanting. It should he decided whether, on 
this point, Spirifer calcaratus, G. Sandberger,'^' which seems to me different 
from the species figured under the same name by Mr. Sowerby, is developed 
to the same extent as this. At the present time I have not the necessary 
material to settle this question. 
Horizon and Localities. — A single rather badly preserved specimen 
has been collected in a grey, very compact limestone in the Yass District. 
3. Spirifer cabedanus, de Verneuil. 
Spirifer cahedaniis, De Verneuil, 1845, Bull. Soc. Geol. France, TI (2), p. 473, pi. 15, fig. 3. 
Shell suhglohose and a little broad, greatest breadth at the hinge line. 
Ventral valve regularly curved, deeper than the opposite one. Beak inflated, 
prominent, incurved and pointed at the apex ; area triangular, rather high, 
with an open deltidium ; cardinal slopes forming an angle a little less than a 
right angle with the lateral ; sinus deep, provided with a very marked median 
fold which starts at the end of the beak. 
On either side of the sinus can he counted twelve radiating ribs, 
rounded, of variable tliickness and also thinner as they occur farther from 
the sinus ; they are separated by deep furrows of the same width as the 
adjacent ribs. Dorsal valve semi-circular in form, beak very small, agreeing 
with the median fold of the sinus of the opposite valve ; lateral folds similar 
to those of the other valve. Growth lines giving rise to the formation of 
small imbricating lamelloe may be seen, princijially on the sides, on good 
specimens. 
* Vide Die Versteinermigen des Rheini.schen Scliicliten Systems im Nassau, pi. 31, figs. 10, 11. 
