160 



great muscles. In another specimen, only a fragment (Fig. 6), 

 the septal cavity is again seen, and similar muscular scars. 

 This was the first example which led me to conceive that this 

 shell might be a Pentamerus, for its resemblance to one well- 

 known cast of the May Hill Sandstone at once caught 

 the eye. 



In PI. 2, Fig. 1, is represented a dorsal valve, in which may 

 be seen the casts of the two septa, enclosing between them a 

 portion of the V-shaped, or fifth chamber, so characteristic of 

 the genus Pentamerus. This is again shown on a more 

 striking scale in Fig. 5, in which we meet with the same 

 characters as to general shape, deflected sides, and front of the 

 shell. It is, however, on one side of the larger hand-specimens 

 that the strong confirmation of the Pentamerus nature of 

 these shells disi^lays itself. We there observe a number 

 scattered about possessing all the features above described, and 

 also one shell split open with the fifth chamber exposed to 

 view, and its sides of that glistening nature so often met with 

 in British examples. (PI. 2, Fig. 7 and 8.) I propose to call 

 this shell Pentamerus Tasmaniensis. 



A fossil, at first sight of a most remarkable nature, may be 

 referred to here. It is an internal cast of two different shells, 

 the Pe7itamerus just described (PI. 2, Fig. 1), and a,8])irifer or 

 an Orthis, probably the latter, a valve of each placed in 

 apposition as if belonging to one individual. On one side 

 may be seen the dorsal valve of the Spirifer or Orthis (PI. 2, 

 Fig. 2), possessing the usual radiating ribs and a smooth medial 

 fold. On the other is what I believe to be a modification of 

 the Pentamerus (PI. 2, Fig. 1), previously referred to. It has a 

 smoother umbonal region, but there is the deflected front 

 sides, the large fifth chamber, and the coarse ribbing. 



On another block is a cast of a well-marked Orthis, a 

 ventral valve with but few ribs, and those coarse and strong. 

 (PI. 2, Fig. 16). In all probability it is the opposite valve of 

 the same species we observed accidentally in apposition with 

 the Pentamerus. It is not unlike Orthis hiforata, Schlotheim, 

 a Middle and Upper Silurian form in Europe. Again, it 

 resembles some varieties of Orthis lynx, Eichwa.ld, a species 

 met with in the Trenton Group of North America. The 

 Tasmanian shell has about seven ribs on each side the medial 

 fold of the ventral valve. 



Another piece of matrix, bearing the number six, has 

 scattered over it numerous small casts of the forms of Spirifera. 

 One is very finely striated, with a wide sulcus, and has all the 

 appearance of the Upper Silnriain Sp. plicatella, Linn., (PL 2, 

 Fig. 9 a and c), or in some points it resembles the young of a 

 Devonian species, Sp. Verneuilii. The second species, although 

 small, possesses strong ribs, like 8p. elevata, Dalm., or 



