BY JOHN" 3IITCHELL AXD W. S. DUX. 



2Gfl 



valve small, straight, moderately inourvecl with a circ-iilar foramen under its ex- 

 tremity, and distinctly separated from the umbone or hinge-line of dorsal valve 

 by a deltidiuui in two pieces, almost surrounding the aperture. Dorsal valve 

 moderately convex and trilobed ; mesial fold extremely narrow at first and sud- 

 denly widening, slightly elevated, flattened along the middle, and sharply separated 

 from the lateral portions of the valve by a deepened groove. The fold is also 

 often bent upwards close to the frontal edge. "\'entral valve almost flat or very 



Text-figs. 1-5. Artypa inarginalis Dahii. Enlarged drawings to show the surface 

 oruaiiientation, muscuhir scars and, in one, greater portion of a spiral. 



sliglitly convex near the beak with a rather deep and sharply defined sinus, mar- 

 gined on either side by a prominent ridge, while the lateral portions of the vahe 

 are gently concave and vertically turned up at the extremity; lateral margins un- 

 dulating; front margin abruptly raised, straight along the middle; surface of both 

 valves ornamented with numerous small bifurcating ridges or ribs." The above 

 description applies to the Australian representatives so fully as to make it un- 

 necessary to give them a separate one. 



In North America this species occurs associated with A. reticularis in Silurian 

 rocks (Niagara Formation), f and is there said by the authors quoted to have been 

 short lived, just as it appears to have been, as far as evidence yet available goes 

 to show, in Australia. 



The discovery of this very remarkaljle Atrypa in Australia is of considerable 

 interest to paleontologists, adding, as it does, another instance of the remarkalile 

 powers for world wide distribution possessed by certain types of brachiopoda. 

 It would appear too, that this species originated in the British Isles and lived 

 there through a longer geological period than elsewhere. In this State it occurs 

 plentifully in the lowest zone of the Lower Trilobite Beds of the Bowning Series 

 on the East and West sides of the Bowning S^Ticline. Its vertical range here 

 seems to be very limited. It is not improbable that it occurs also in the Orange 

 district, for the fossil described by one of usf under the name of Camarntecli/ia 



•Hall and Clarke, Pal. N.T.. vol. iii., Brachiopoda. pt. ii., p. 173. 



tDun. Rec. Geol. Surv. N.S.W., viii.. pt. 3, 1907, p. 127, PL xl., figs. 3, 3b. 



