9 



posterior ventral margin, rounded, gradually curved towards 

 small oblique posterior lobe. 



Length, 11 millimetres ; height, 14 mil. 



Common Upper Marine Beds (Upper Pal.), Mersey. 



Family Peotinid«. Genus Aviculope ctett . (McCoy.) 



Shell id equi valve, suborbicular, eared ; hinge-areas flat, with 

 several long narrow cartillage furrows, slightly oblique on each 

 side of the umbones ; right valve with a deep and narrow 

 byssal sinus beneath the anterior ear; adductor impression 

 large, simple, sub-central ; pedal scar small and deep beneath 

 the umbo. (Tryon J 



AviCTTLOPECTEN DlEMENENSIS. (NOV. Sp.) 



Shell large, truncate-orbicular depressedly, convex ; ears 

 unequal, the posterior one of moderate size, obliquely tri- 

 angular, somewhat concave ; the anterior one large, subovate, 

 flattened or slightly convex, separated at the margin from the 

 body by a deep and acutely rounded sinus ; surface of both 

 ears and body of shell marked with numerous, rather sharp 

 concentric lines of growth, between which there are numerous 

 microscopic wavy concentric striae ; the body is ornamented 

 with about 22 simple raised ribs radiating from umbo to 

 margin, where they are somewhat broader ; the interspaces are 

 deep and somewhat narrower than the ribs, and there are 

 eight of them posteriorly, which broaden out towards margin 

 and are divided by a fine ridge ; the ribs and channels become 

 shallower as they approach the sides ; both ears are similarly 

 ornamented with regular, simple, radiating ridges. 



Length, 3| inches ; breadth, 3| inches. 



Upper Palaeozoic mudstones, Maria Island. 



Ayicueopectest Speentii. (nov. sp.) 

 Shell truncate-orbicular, longer than wide, slightly convex ; 

 ears comparatively large, sub-equal and symmetrical, broadly 

 wedge-shaped, slightly convex ; both ears are separated 

 from body of shell by a moderately deep sinus, that 

 under the anterior ear being more acute ; there are 

 close, faint, concentric lines of growth on the ears, and 

 body of shell producing an obtusely granular appearance 

 upon the regular flatfish radiating riblets ; there are only about 

 15 riblets running from umbo to margin, towards which they 

 gradually increase by a furcated division of the broadening, 

 intervening spaces ; generally at the extreme margin there are 

 from two to three liner secondary riblets between each primary ; 

 each of the secondary spaces again are faintly divided near 

 extreme margin by a tertiary riblet. 



