ofQ 



443 





[Form with vibraculoid setce: Britain, chiefly south and 

 south-west coasts; France (south-west), Mediterranean, Ma- 

 deira, Gulf of Florida]. 



Some beautiful varieties of this variable species occur : the 

 form which bears vibraculoid setse is especially remarkable for 

 richness of sculpture and delicacy of structure ; it is furnished 

 with a distinct (though minute) lunate pore, placed within the 

 triangular space below the mouth. This character therefore 

 is not distinctive as between the genera Microporella and 

 Cribrilina, though it is always present in the former and very 

 exceptionally in the latter. Smitt unites these genera in one 

 family (Eschariporidae *) ; but the very peculiar structure of 

 the cell-wall in Gribrilina seems to entitle it to stand as the 

 type of a separate group. 



Family Microporellidae, 



Microporella, Hincks. 



Microporella ciliata, Pallas. 



Normal and forms californica (Busk), vibraculifera and 

 nmbonata, mi hi. 



[Normal : Arctic and northern seas j Britain, France (south- 

 west), Mediterranean, Florida, Zanzibar, Australia, New Zea- 

 land, &c. Var. californica, California.] 



Microporella ciliata, form vibraculifera f, n. 



(PI. XVII. fig. 2.) 



Avicularium replaced by a very tall membrano-chitinous 

 vibraculoid process, situated on a rather large mound or 

 swelling, the beak elevated at the sides and somewhat deeply 

 notched or channelled at the extremity. 



This is in many respects the most remarkable form which 

 Dr. Dawson's dredgings have yielded. It occurs abundantly 

 and in company with the normal M. ciliata and several inter- 

 esting varieties. 



I have already discussed (in the paper referred to) the 

 curious morphological change which the avicularian organ has 

 undergone in this variety, and its significance as illustrating 

 the relation between the two appendages (avicularium and 

 vibraculum). The mandible of the avicularium is frequently 



* ' FloridaB Bryozoa/ part i. p. 21. 



t See a paper by the author (i On certain remarkable Modifications of 

 the Avicularium in a Species of Polyzoon j and on the Eelation of the 

 Vibraculum to the Avicularium " (< Annals ' for January 1882, p. 20). 



30* 





