270 TlIK ATKYPILUK OF NEW SOCTH WALES, 



sussmilchi may be iilentioiil with this species. In En<rlan<l it seems to range from 

 Lower to middle Upper Silurian. In our Bowning rocks it is found associated 

 with Encrinurus silverdalensis E. & M., E. mitchelli Foerste and below beds con- 

 taining Odontopleiira howningensis E. & M., O. parvissima, E. & M., (Jeratoce- 

 phula vogdesi E. & M., and these rocks are not younger than those of Wenlock 

 age. The occurrence of this small Atriipa at such a distance from places where 

 pre\'iously found will no doubt be of much interest to geologists, and may help to 

 indicate the route along which Palaeozoic marine faunas were distributed from 

 Europe to Australia or vice versa. 



The first record of its presence in Australian rocks appears to have lieen 

 made by one of us.* 



Loc. and horizon. — Silverdale, Parish of Derrengullen, County King; and one 

 mile south of Bowning Public School. Parish of Bowning, County Harden. 

 Lower Trilobite Beds, Bo^vning Series. 



Atrypa pfLCHRA, n.sp. (PL xiv.. tig. 19; PI. xvi.. tig-s. 14-lf).) 



Shell subdiseoidal or rarely oval, biconvex, radial ami concentric striae very 

 fine, and form a beautiful caucellate pattern ; marginal Iriuge very narrow, and 

 mildly recurved, hinge line arcuate, front margin very mildly sinuate. Pedicle 

 valve about as convex as the brachial valve, from the umbo for two thirds of its 

 lengfh medially decidedly ridged, and opposed to this in the brachial valve is a 

 shallow sulcus; benk moderately prominent, mildly incurved, foramen conspicuou-^ 

 iuid circular. Brachial valve evenly and moderately to fairly strongly convex 

 in adult specimens; sulcus faint and vanishes as it reaches the middle of the valve. 

 Dimensions of an adult specimen — length and width, 15.4 mm., depth, 9.4 mm. 



Obs. — This species differs from the .1. reticularis in (1) its small size. (2) 

 exceedingly fine ornamentation, (3) approximately equal biconvexity of the 

 valves, (4) greater prominence of the beak of file pedicle valve and of its fora- 

 men, (5) its uniformly subcircular outline. (6) very narrow marginal fringe. 



We have no specimen showing internal structure, but from external eviden^'e 

 we assume it to closely resemble that of A. reticularis in this particular. The 

 specimens of this species used for the present description were obtained chiefly 

 from the upper of the lime.stone beds of Limestone Creek, Silverdale, immediately 

 below the Lower Trilobite Beds of the Bowning Series, and were associated with 

 numerous corals representing the genera Favosites, Heliolites, CiMtliopIiiillum and 

 Tryplasma and with .1. reticularis, etc. The vertical range of this fossil is ap- 

 parently limited. 



I^dc. and hnrizoH. — Limestone Creek, Silverdale. near Bowning, Parish of 

 Derrengullen, County King. Probably Wenlock. 



Atrypa DrxTROONEXsis, n.sp. (PI. xvi., figs. 8-12.) 



Shell almost equally biconvex oval, radial ribs subsharply ridged, not pro- 

 minent, dichotomise two or three times, concentric striae fine and very numerous 

 and undulating towards the front. Pedicle valve moderately convex throughout, 

 slightly upturned at the margins, umbo and beak not prominent, the latter de- 

 pressed. Bracliial valve slightly more tumid than the other, muscle scars incon- 

 spicuous, the margin in front very slightly sinuate. Dimensions: Length, 10.7. 

 width, 17, depth 11 mm. These dimensions are for mature specimens. 



•Mitchell, Proo. Aust. Assocn. Adv. Sc, i., 1887 (1888), p.293. 



