BRITISH PALJEOaENE BETOZOA. , 241 



appears to be Schizoporella gonversi (Eeuss) [No. 14, p. 159, pi. vii. fig. 7], from 

 Rauchstallbrunn, but in that species the zocecia are shorter and broader, the areolae, 

 fewer, and there is a pair of avicularia above the aperture. 



The large size of the sinus allies this species to Schizoporella beyrichi, Stol., but it 

 differs in that the zocecia are elongate and rectangular instead of hexagonal, they are 

 not quincuncially arranged, and the zoarium is not Cellarian {Cellaria heyrichi, Stoliczka, 

 No. I, p. 83, pi. i. fig. 10). 



ScMzoporella insignis, Hincks [No. 4, pt. 5, p. 134, pi. v. fig. 10], differs in the 

 quincuncial arrangement of the zocecia, the central umbo, and the raised line at a little 

 distance from the margins of the zocecia. The shape of the zocecia and the absence of 

 the tubercles above the aperture distinguish this new species from iS'. paitper (Eeuss) 

 [Lepralia pauper,'Re\iss,, No. 14, p. 164, pi. v. fig. 4], which has a large sinus. The 

 last two species with which it is necessary to compare this are S. variabilis (Reuss) 

 [Hemeschara variabilis, Reuss, No. 12, p. 508, pi. i. figs. 1-5] and S. unicornis (Johnst.) 

 [Lepralia unicornis, Johnston, No. 2, p. 320], which both belong to the same group. 

 From the former the London Clay species is mainly to be distinguished by the size of 

 the sinus. The latter differs by its umbo, the absence of maculae, and the smaller 

 aperture ; the zocecia, however, agree in general form. 



IV. a. The Systematic Position of the Adeonellidse. 



The genus Adeona was established by Lamouroux [No. i, pp. 478-482, pi. xix. fig. 2] 

 in 1816 for some Bryozoa with short jointed stems and reticulate zoaria ; he took 

 an Australian species, A. grisea, as his type : this species has also been made by 

 Macgillivray the type of a genus Bictyopora, which is therefore necessarily a synonym. 

 Enlarged figures of the zocecia have been given by Kirchenpauer [No. i, pi. i. fig. 8, 

 pi. ii. fig. 10] and Macgillivray [No. i, pi. 66], and these show that it possesses a trypa 

 or zocecial pore and a simple holostomatous orifice, and must therefore be referred to 

 the Microporellidse. But this genus and its allies have long given much trouble to 

 systematists and the classification is still unsettled. Busk's ' Challenger ' Report must 

 certainly be held responsible for much of the confusion, as he there founded a genus 

 Adeonella based wholly on zoarial characters ; in consequence he included in it a 

 miscellaneous series of species that must be divided among the several genera. Thus 

 his Adeonella distoma has a trypa and is one of the Microporellidse, while others, such 

 as A. polymorpha, have no such pore and must belong to a different genus and family. 



The subject has been attacked by Messrs. Hincks, Waters, and Macgillivray, and 

 each of these has advocated very different conclusions. Mr. Hincks [No. 8, pt. i. 

 pp. 150-158, especially 155 & 157] has discussed the matter at length with the following 

 results : he maintains (1) that as Adeonella is based only on zoarial characters it is not 

 distinct from Adeona ; (2) the latter genus he places among the Microporellidse, distin- 

 guished from Microporella by the substitution of gonoecia for external ooecia ; (3) as he 



