1911.] 



NATURAL SCIENCES OF PHILADELPHIA. 



491 



Except for the sutural bristles, the girdle is stated to be nude, 

 but examination of specimens mounted in xylol or balsam and 

 especially dissolving fragments in Javelle water shows that the 

 condition is approximately the same as in D. thamnopora, although 

 the spicules are even smaller than in that species. In none of the 

 specimens seen were the bristles still adherent at all of the sutures. 

 Usually they are lost except around the posterior valve, and even 

 here they are rarely unbroken. When complete they are longer 

 than in the preceding species, more slender, lack any appearance of 

 surrounding hairs at the base and give off shorter and less numerous 

 recurved processes. Originally there seem to have been one bristle 

 opposite each suture, from two to five in front of the head valve, 

 and two behind the tail valve. There is no mention made by Pilsbry 

 of intersutural tufts, but I find that very small inconspicuous bristles 

 are sometimes evident in the centre of the round whitish spots which 

 are to be seen about the periphery. Although so greatly reduced 

 they seem clearly homologous with the structures holding a similar 

 relation in the preceding species. 



The color ornamentation is described by Pilsbry as follows: 

 "(1) olive-green with some lighter spots, or purplish maculation, 

 or slight roseate suffusion, or (2) vivid red, with scattered blue 

 spots." With one exception my specimens are all of the latter type, 

 agreeing with one another further in that valve VI, and to a less 

 extent valves V and VII, are irregularly clouded with a pale greenish 

 hue. 



The nine specimens I have seen are doubtless all immature. 

 Length of largest 11 mm.; width 7 mm. 



Type: No. 71,902, A. N. S. P. 



Type locality: Monterey Bay, Cal. (H. Heath, 1897). 



Specimens examined : 



Thiele has suggested that Mopalia heathii may be a Ceratozona, 

 but although it is certainly suggestive of that genus in several ways, 

 I fail to see that it does not show equally significant approximation 

 to the group in which it was originally placed. The truth is that 

 the diagnosis of either genus, as previously recognized, would have 



