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Inside and form. — After disarticulating a series from the various localities, 

 the shape and carination of the valves, the position of the mucro on the tail valve, 

 and the shape of the sutural laminae were so similar as to need no special com- 

 ment. The variation of the number of slits in the insertion plates of the two 

 end valves is interesting but not conclusive; thus Sydney specimens showed 12-12 

 slits. Port Arthur 11-12, Penguin 11-12, Marino (South Australia) 10-10, Yal- 

 lingup 10-9. But another from Marino showed several additional, crowded slits 

 in the tail valve, while still maintaining the 10 in the anterior; also a large shell 

 from Yallingup has 10-12 slits. The most that can be said is that the South 

 Australian and the Western Australian shells both seem, when of an equal size, 

 to have a fewer number of slits than is the case with the eastern forms. 



Sculpture compared. — The Sydney shell is decorated with very shallow sub- 

 triangular pits, which are more evident in the pleural area than in the lateral ; 

 concentric growth sulci are present in the lateral areas and are continued across 

 the pleural. The girdle is covered with polished, smooth, pebble-like scales, 

 features that are common to the whole series referred to above. The specimens 

 from south-eastern Tasmania are generally similar in sculpture, which is very 

 shallow, the pitting in the pleural area is to some extent arranged in longitudinal 

 rows, the shallow ridge between these when seen under 65 magnifications, and 

 laterally lighted, gives the effect of longitudinal ribbing, a feature I have not 

 noticed in the shells from Sydney, the growth sulci are present in the lateral 

 areas but only to a very limited degree in the pleural; a juvenile from this 

 locality, 10 mm. in length, is completely smooth except for growth sulci. The 

 .specimens from north-western Tasmania are very similar, although, possibly, the 

 lateral area is smoother, the inner half often absolutely smooth, and the pitting 

 in the pleural area is circular and more evenly distributed than the preceding, 

 but still very shallow. 



All the South Australian shells, whether they be the variety with delicate 

 streaking, described as H. resplendens, or of any other pattern, show a dis- 

 tinctly deeper pitting, which is much more regular than any of the preceding, 

 the pits in a few pilaces are confluent, but on the whole are so regular that the 

 ridges between, under a high power, resemble a network or honey-comb. In 

 the shells from Yallingup, in Western Australia, this regular honey-comb pitting 

 reaches its maximum development. In the pleural area, in both younger 

 and older shells, the pitting is regular, deep, circular, or hexagonal, and the same 

 character is preserved in the lateral areas, except that it is there a little confused 

 by a limited amount of radial pitting. While some wavy growth sulci cross the 

 lateral areas and are to a small degree seen in the pleural, they are not in evidence 

 to anything like the extent that they are in the far-eastern forms. The scales in 

 these western specimens are larger than in any of the preceding, but this may be 

 partly due to their much larger size. 



In conclusion. — Radial ribbing or shallow grooving in the two end valves 

 and lateral areas is present in all Yallingup specimens, and in all medium to large 

 specimens from South Australia, but is absent in those from New South Wales 

 and Tasmania. I have one partial exception from the latter State, in which two 

 of the valves are abnormal ; in these, this feature is merely suggested. 



The pitting in the eastern shells is more shallow, and in some parts absent 

 altogether, and the juvenile specimens are often quite smooth, which is never the 

 case with the western forms. 



I therefore propose to recognize H. resplendens, of Bednall and Matthews, 

 as a subspecies, including under this name all the varieties occurring in South 

 Australian waters. One hardly knows what to do with the Yallingup form. It 

 certainly exhibits a wonderful constancy in colour and pattern, and shows the 

 distinctive sculpture of the South Australian shell in its most marked degree; 



H 



