General History of the Marine Polyzoa. 87 



accounted distinct. Busk describes two varieties of his species, 

 one with a crustaceous the other with an erect habit of 

 growth. It is with tlie former (var. incrustans) that he 

 identifies tlie Madciran species. Tlie points of difference are 

 the much more robust and massive character of M. crassi- 

 marginata, tlie unusual thickness and strong crenation of the 

 cell-margin, the depth of the cell-wall, which can be seen 

 in the interspaces between the zooecia, and the form of the 

 avicularian cell, which is perfectly oval, like the zooecium, 

 and bears a straight mandible, rounded at the extremity, whilst 

 that of Busk's species is " broadly spatulate." The general 

 character of the cell in il/. crassimarginata presents a contrast 

 to that of the ' Challenger' form, which is heightened by the 

 entire absence in the latter of its most marked feature — the 

 broad, deeply cut (crenated) margin. 



Busk gives Bijlustra Lacroixii of Smitt (^ Floridan 

 Bryozoa,' pt. ii. p. 18) as a possible synonym of his 

 var. incrustans. It may be so, but it is certainly not the 

 Madeiran species. 



Ibid. (p. 6 Sep.). 

 Cribrilina radiata^ Moll, var. 



Busk in his description of Madeiran Polyzoa in Quart. 

 Journ. Micr. Sci. vol. vii, (1859), figures a variety of G. 

 radiata which agrees in most respects with the above, and 

 notably in the remarkable elongation of the avicularium. In 

 the same volume of the Micr. Journ. he records the occurrence 

 of Lepralia PouiUetii, Aud., and remarks that it is readily 

 distinguished from 0. i-adiata " by the absence of the large 

 avicularia and the uniformity of the front of the cell." 



But the avicularium is very commonly absent in C. radiata^ 

 and when present exhibits many varieties of form. The 

 front wall, too, is liable to much variation, especially in the 

 character of the transverse ridges and central keel"^. When 

 the keel is absent and the transverse ridges are but slightly 

 developed the cell presents the appearance represented in 

 Audouin's Flustra Fouilletii^ which must certainly rank as 

 one of the synonyms of C. radiata, Moll. 



There is also a good deal of variability in the superficial 

 characters of the ooecium, which does not seem to have 

 attracted much attention. Savigny figures in Flustra 

 PouiUetii a simple raised line passing backwards from the 

 centre of the oral arch. In a form figured in my ' History ' 



* See my 'History of the Brit. Marine Polyzoa/ j-p. 187-189, and 

 pi, XXV. tigs. 1-9. 



