General TTtstory of the Marine Polyzoa. 171 



laviuin of peculiar form and structure, instead of the small 

 central one below the orifice, and the frequent occurrence of 

 a second avicularium simihir to the last-named on the lower 

 part of the front wall. The pore, we now know, is liable (as 

 in Microporella decorata) to very considerable variation within 

 the limits of a sjiccies. Tiie oblique direction of the suboral 

 a\iculariuni, on which Busk founded his Lej)ralia plufjiopora, 

 is, as I long since pointed out, a character of very small 

 moment. The occurrence of the second small avicularium 

 would hardly merit notice were it not the case that in A. vio- 

 lacea, as commonly met with, there is a remarkable constancy 

 both as to number and character in this appendage. Amongst 

 the large number of British specimens examined 1 have never 

 met with any diversity of shape, a fact which gives more 

 significance to the presence of the gigantic avicuUirium, with 

 its elongate beak and scimitar-shaped mandible, than it would 

 otherwise possess. It may be regarded as probably a local 

 adaptive modification of the ordinary suboral form, which 

 is always absent from the cells bearing the large lateral 

 avicularium. 



So far the latter has only been noticed on specimens from 

 the Indian Ocean. When present it produces a remarkable 

 change in the appearance of the zooecium, which is much 

 widened above, the increase being entirely on the avicularian 

 side and being due to the presence of the large avicularian 

 cell. The long curved beak is also carried up for some 

 distance, causing an extension of the zooecium above. The 

 transformation of the avicularium in some of the cells of a 

 colony (as in Smittia nitida^ Yerrill, p. 46 sep.) is of not 

 uncommon occurrence ; but I cannot recollect a case in which 

 it so materially affects the aspect of the zooecium. 



A question arises as to the true specific name of the A. 

 violacea, Johnston (sp.). In her 'Synonymic Catalogue' 

 Miss Jelly records it as Microporella IJeckeli, Reuss, on the 

 ground that Reuss described it in 1847 and Johnston in his 

 second edition, bearing date 1849. This is an error, and I 

 regret to say that I am responsible for it. In the Bibliography 

 at the close of my Hist. Brit. Mar. Polyzoa, through an 

 oversight in correcting the proof, 1849 is given as the date 

 of Johnston's second edition, which was really published in 

 1847, the same year as that in which Reuss's Pol. d. Wiener 

 Tertiiirbeck. appeared. Johnston's preface is dated April 

 1847, and unless it can be shown that the German author's 

 book was published earlier in the year, there is no ground 

 whatever for the change. 



It is not probable that Johnston's claim will be disputed. 



