10 



Some of the specimens attain a considerable size as indicated 

 by fragments. The specimen from which the description is 

 taken is about 30 millimetres long, and 30 mil. broad. 



Common in Upper Palaeozoic sandstones, Porter's Hill, 

 Hobart. 



In the larger fragments the radiating spaces between the 

 fine, rounded, primary riblets seem to be bracketed together as 

 a group by the wavy transverse striae, which are also slightly 

 arched between each primary riblet. 



AVICULOPECTEN HoBAETENSIS. (NOV. Sp.) 



Shell truncate-orbicular, wider than long, flatly convex ; ears 

 widely expanded, somewhat unequal — the posterior one 

 obliquely triangular, slightly concave ; the anterior one flatly 

 convex, cuneate, separated from the body of shell by a deep, 

 obtusely angled sinus ; surface of ears and body of the shell 

 smooth, marked with a few obtuse concentric lines of growth, 

 and radiated by numerous fine, rounded riblets, more or less 

 regular and simple ; the intervening spaces or channels nearly 

 equal in width to riblets ; there are about 56 riblets near 

 margin 



Length, 53 millimetres ; breadth, 45 mil.; length of hinge 

 line, 49 mil. 



This is a very distinct form, although at first sight it re- 

 sembles A subquinque-lineatus, from which it is distinguished 

 by its greater relative breadth, and the fineness and regularity 

 of the riblets. 



One specimen from Upper Palaeozoic sandstones, Porter's 

 Hill. 



Ayicueopecten' Lateobensis. (NOV. sp.) 



Shell sub-orbicular, slightly convex, a little longer than 

 broad; ears small, small, sub-equal ; the posterior one is the 

 smallest and is obliquely wedge-shaped ; the anterior ear is pro- 

 duced into a sharply-pointed wing, and is separated from the 

 body of shell by a deep obtuse oblique sinus ; both ears and 

 body of shell are ornamented by regular and somewhat sharply 

 imbricated rays ; on the body there are about 21 rays pro- 

 ceeding from umbo to ventral margin, separated by channels 

 of about the same width ; each channel is divided by a fine, 

 slightly raised riblet, thus forming a regular alternation of large 

 and small riblets. Prom the appearance of the inner face of 

 the valve, it would seem probable that the outer surface of 

 these imbricated ribs is somewhat squamose, and is more pro- 

 nounced at distant intervals corresponding with concentric 

 lines of growth. 



Length, 46 millimetres ; breadth, 43 mil. Occurs with 

 Spirifera Tasmaniensis and Plourotomaria Woodsii, in the 

 Marine Tasmanite bed at the Mersey. 



