312 SIDNEY F. HAh'MER. 



Calwellia sinclairii,^ Busk (fig-. 60). 



Waters (1888, p. 17) has described the compensation-sac 

 in this species, as well as in C. bicornis and Urceolipora 

 dentata, and he correctly states that it opens to tlie exterior 

 b}' moans of the median pore. I agree witli Waters that 

 C. sinclairii should be placed in the genus Calwellia. It 

 differs from C. gracilis principally in the fact that the 

 proximal half of the zooecium is almost as broad as the 

 distal half, and the zooecia do not therefore appear to 

 be so definitely arranged in pairs. 



The operculum is a segment of a circle somewhat greater 

 than a semicircle, and having a straight base-line. From the 

 middle line of this a longitudinal suture (.s.) passes to the 

 transversely elongated median pore [m..'p.), and on each side 

 of the suture is a round fenestra. The suture can usually be 

 traced down the entire length of the zooecium. The position 

 of the lateral horns of C. gracilis is indicated by a fenestra 

 (/.), in the neighbourhood of which are one or two smaller 

 pores. The median pore is somewhat crescentic, with an 

 anterior concavity. The lateral edge of the large compensa- 

 tion-sac does not pass to the base of the operculum, but turns 

 sharply inwards at the level of the median pore, and i-uus 

 into the broad tongue-like lobe of the wall of the zooecium 

 which gives the pore its crescentic form. 



The operculum has a well-marked triangular lobe of its 

 vertical marginal flange (/.), into the apex of which the 

 occlusor muscle is inserted, as in Flustra. 



Calwellia dentata,- MacGillivray. 



It appears to me that this species should be separated from 

 U. nann,""^ and placed in Calwellia, the generic character of 

 which would then liave to be amended so far as relates to the 

 arrangement of the zooecia. In C. dentata these are placed 



' Busk (1884), p. 103. 



- ' Prodr. Znol. Vict.,' Dec. xi, 1885, p. 19. 



' As suggested by Waters (1888, p. 10). 



