235 



and more or less coalesced and irregular. On the sides, corresponding with the 

 pleural area of the median valves, these much-elongated granules are formed into 

 longitudinal rows. The posterior half of this valve is much raised and decorated 

 with twelve rays or flutes, of which the two anterior ones are much the strongest. 

 The whole of this area is covered with round, white granules. Inside. — 

 Transparent white, sinus broad, sutural laminae straight and parallel with teg- 

 mentum, slits 10, mostly opposite the ribs, the outer two having no corresponding 

 slits. 



Median valve. — The dorsal area is broadly wedge-shape and covered with 

 white granules, which are small towards the apex but rapidly increase in size 

 anteriorly and laterally, those adjoining the pleural area are long and finger- 

 shaped ; there does not seem to be any system in the arrangement of the grains 

 in the dorsal area. The pleural area is very distinct, being decorated with bowed 

 longitudinal rows of white granules ; the five next the dorsal area composed of 

 small, round, detached granules, whereas the outer five rows have extremely 

 elongated, white, finger-like granules, which are more or less coalesced into high 

 granulose ribs, which are increasingly raised as they approach the girdle. The 

 ribs are widely spaced, but there is no indication of any bridging or net-work, so 

 characteristic of Callistochitons. The lateral area is proportionately very 

 narrow, composed of two very strongly-raised ribs, the anterior more raised than 

 the posterior, with a deep sulcus between them, the whole of this area is covered 

 with small, rounded, white granules, but towards the outer margin there are 

 several masses of elongate, coalesced, widely-spaced, white granules, the posterior 

 margin of these valves is irregularly toothed with very similar elongate pro- 

 cesses with rounded ends, becoming coarser towards the girdle ; the anterior 

 margin is also toothed, many of them being double-headed. Inside transparent 

 white, the tegmentum is folded over and in valve 2, pleated under the beak, 

 sinus broad and edge bowed forward, sutural laminae shallow, waved inwards, 

 edge in some is parallel with tegmentum, in others slightly rounded, slits 1-1, 

 broad, sharp cut, straight-sided, eaves well defined, insertion extending beyond 

 the tegmentum. 



Girdle. — The girdle is very broad in proportion to the size of the shell, 

 being 125 mm. in width, is clothed with flat, thin, fluted, imbricating scales, 

 the scales are subpointed and have 6-7 grooves, the ribs between the grooves 

 being shallow and flat. The scales are thinner than and quite distinct from 

 those of any Callistochiton I have seen. 



Measurement. — The dry specimen measures over all 7X4^ mm.; as the 

 girdle is only in one part uncurled, and there measures 125 mm., the living 

 animal would probably be | mm. broader. 



Habitat. — Carnarvon, in the extreme north of Shark Bay, Western Aus- 

 tralia, collected by Mr. Worsley C. Johnston, to whom I am greatly indebted 

 for the specimen. 



In conclusion. — As before stated, I have had great difficulty in deciding 

 whether this species is distinct from Thiele's Callistochiton recens, for, although 

 the most unusual and striking characters present in the shell under review are 

 not mentioned at all by Thiele, there is always the possibility of such features 

 being undeveloped in a very juvenile specimen. But after making every allowance 

 for the difiference in the size of the two specimens, it seems impossible that these 

 characters could have been overlooked by Thiele. I append a short resume of 

 the correspondence and diflferences between the two descriptions. As before 

 stated, the fact that Thiele did not figure C. recens has added greatly to the 

 difficulty. 



