BY JOHX MITCHELL AXD W. S. DUK. 271 



Obs. — Among specimens forwarded by the late Rev. W. B. Clai-ke to the 

 late Rev. Sedgwick in 1844* from Dimtroon, N.S.W., Salter reported having 

 recognised Atrypa reticularis Linn. We are of the opinion that the shell 

 now under review is specifically identical with the one referred to by Salter. 

 It certainly bears some resemblance to the normal A. reticularis, and on first in- 

 spection we were inclined to make it a variety of the normal form but on closer 

 study of it, determined to give it specific rank. From A. reticularis it differs in 

 having the valves almost equally convex, little or no foliated margin, very fine 

 wavy and numerous concentric striae, no defined sulcus in either valve, slightly 

 sinuate margins, and the length invariably gi'eater than the width. In some re- 

 spects this species resembles A. (?) headii Billings var. anglica. Found asso- 

 ciated with Encrinurus duntroonensis E. and M. and Trinuclem clarkei Mitchell. 



Loc. and horizon. — Near Duntroon homestead. Parish of Canberra, County 

 jMurray . 



Atkypa desquajiata Sowerby. (PI. xv., figs. 12, 13.) 



This species was recorded by de Koninck from New South Wales, but no 

 particulars of locality were given. 



Specimens of the species have been collected from the black cave limestone 

 beds of Cave Flat, and Goodravale, Parish of Woolgarlo, County Harden, and the 

 Tarago District, by officers of the Department of Mines, Sydney, and one of us, 

 and it will be noticed, on reference to our figures given of a specimen of the local 

 form, that it agrees with the Euroj^ean types. 



Atrypa plicatella de Koninck. 



This species was said to have been found in a black limestone in Yass district.f 



No subsequent reference seems to have been made regarding the occuiTence 



of this species in New South Wales rocks. Judging by the figures and description 



we are not disposed to accept de Koninck's determination. Externally it bears 



little if any resemblance to an Atrypid. 



Atrypoidea, n.g. 



Geii. chars. — Shells strongly biconvex and at maturity some forms ovoid to 

 globular, not conspicuously inequivalve, surface smooth, but sometimes very 

 faintly showing concentric growth lines. Beaks not prominent, hinge line 

 straight and moderately long; cardinal angles high and rounded. Pedicle, valve 

 less convex than the brachial, with or without a faint sulcus, beak of the pedicle 

 valve relatively small, depressed and incurved. Foramen apical and circular in 

 mature specimens. Anterior margin moderately to very intensely sinuate. The 

 deltidial plates and teeth have not been observed. Muscle scars appear to be 

 large and moderately defined. Brachial valve very convex, no defined median fold 

 except in cases of mature specimens in which, towards the front, a short fold is 

 sometimes developed, but sometimes bearing a very faint medial sulcus. No 

 cardinal area, beak incurved and concealed. Crura unknown. Brachidia or 

 spirals form cones, consisting of about ten volutions in specimens reaching two 

 thirds maturity. The apices of the cones are directed towards the centre of the 

 brachial valve cavity, but in one or two cases they had a droop anteriorly which 

 may have arisen from accidental causes. 



'Ofi. cH. 



Me Koninck, Mem. Geol. Siu-v. N.S.W., Pal. Xo. (i, 1898, p. 78, PI. iii., figs. 4 and 4rt. 



