BY R. ETHERIDGE, JUN. 209 



sometimes a little oblique ; sinus very faintly shown on the surface 

 of the valve, but indicated by a forward extension of the front 

 margin. Dorsal valve moderately convex, evenly rounded in 

 outline, with little or no distinction into fold and flanks ; umbonal 

 region far more marked than in the ventral valve. Surface of 

 both valves with coarse, concentric, roughened laminae. 



Obs. — ^A very i)eculiar form of Athyris, from the persistent 

 shallowness of the united valves, especially of the ventral. 

 Ordinarily in this genus the valves are equally convex, or the 

 ventral valve is the more so, the perforated umbo of the latter 

 overhanging that of the dorsal valve. There is also a sinus in 

 the ventral, and a fold more or less developed in the dorsal. In 

 A. Macleayana some of these characters are reversed, thus : — 

 the ventral valve is almost flat, except just at the front margin, 

 the latter being bent upwards, and so representing the sinus. 

 There is no fold in the dorsal valve, but it is moderately convex, 

 and there is a sinuated front margin to some extent. The umbo 

 of the ventral valve does not curve over that of the dorsal as in 

 most species of Athyris ; but, on the contrary, what little umbo 

 there is to that valve is to some extent truncated, and the fora- 

 men is practically at right angles to the hinge line, instead of 

 opening in the same plane. From this arrangement die foramen 

 appears to open upwards, and is inconspicuous. In other words, 

 the ventral valve fits on to and against the dorsal ; and when the 

 united valves are held in a direct line, and on the same level with 

 the eye, from the dorsal side the foramen is not visible. These 

 characters are constant in all specimens examined by me, and are 

 so contrary to the general features in Athyris that I feel obliged 

 to separate this curious shell as a distinct species. It affords me, 

 therefore, much pleasure in associating with it the name of Mr. 

 Macleay, to whom I am indebted for an opportunity of describing 

 these interesting fossils. 



In one or two places the appearance of the concentric surface 

 laminae would lead to the belief that they projected as separate 

 spines, after the manner of Athyris Roysiiy Lev. 

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