CORBITELLA AND HETEROTELLA. 21 



tolerably regularly eheckered lattice-work. The meshes of the 

 lattice-work contain each a parietal osculum. This is circular, 

 measures up to 2 mm. in diameter and is separated from nearest 

 neighbors by a space of 2-3 mm. Nowhere in the specimen is 

 the ankylosis of spicules observable. 



The spiculation of this specimen will be described in detail, 

 after we have dealt with the two other specimens. 



Specimen B. This bears the labelling " Alcyoncellum cor- 

 bicula. Bourbon. M. Sachet. 1857. "* It is the complete specimen 

 of which an account was first given by Bowerbank in '67, p. 

 359, who held it as specifically different from all other specimens 

 bearing the same name in the Paris museum. A very good 

 figure of the same specimen, prepared after a photograph, was 

 shortly afterwards given by Gray ('67, fig. 2) and also by W. 

 Thomson ('68, fig. 1) together with a description based on 

 original observation. As this specimen, besides being entire, 

 differs somewhat in general appearance from Specimen A, a special 

 description will not be out of place. 



The sponge is tubular, shaped somewhat like a glass-tumbler, 

 abrupty truncated above and somewhat tapering downwards. In 

 the upper part it is roundish in cross-section ; iuferiorly it be- 

 comes four-cornered, finally to become compressed at the base. 

 At this end the wall is broken through but is furnished in parts 

 with a few knob-like points of attachment to a hard substratum. 

 Total length of body 105 mm. Greatest breadth, close to the 

 upper end, 92-96 mm. 



* The wording on the label as given by W. Thomson ('68, p. 131) should run some- 

 what differently. Either the labelling has since been changed or W. THOMSON did not 

 quote correctly, perhaps by a slip of memory. 



