232 J- Playfäib McMubrich, 



in individuals whicli liad a fifth cycle of tentacles some exceedingly 

 small representatives of a fourth cycle of mesenteries, biit they did 

 not form a complete cycle, nor, indeed, were they always distinguish- 

 able in tliose portions of tlie colimin where tentacles of the fifth 

 cycle were present. Frequently the fiftli cycle tentacles were much 

 crowded against the adjacent fourth cycle ones and appeared to 

 arise from the bases of the latter rather than directly from the 

 disc and in such cases no corresponding mesenteries could be ob- 

 served. 



It would seem that in this species there is presented an in- 

 stance of a form in which a reduction of the original number of 

 mesenteries had taken place. The reduction has effected an almost 

 complete obliteration of at least one cycle of mesenteries and has even 

 affected the development of the second cycle. Instead of regarding the 

 small number of perfect mesenteries and the relatively low total number 

 of mesenteries as primitive, I would prefer to consider the species 

 as a degenerated form derived from ancestors possessing a greater 

 number of completely developed mesenteries. 



The longitudinal muscles, when developed, form strong pennons, 

 the processes ending somewhat abruptly at the inner edge, though 

 tapering gradually externally (Figs. 12 and 13). The parieto-basilar 

 is represented but does not form a fold. The majority of the in- 

 dividuals examined showed no reproductive elements, but in the largest 

 one (Talcahuano) they were present in the mesenteries of the second 

 and first cycles, including the directives. Both oral and parietal 

 stomata were present and there was a weak basilar muscle having 

 the form represented in Fig. 15. 



I was inclined for a time to refer this species to the genus 

 Gondylanihus of Caelgren (1899), but the fact that the rudimentary 

 mesenteries in Caelgren's C. magellanicus were confined more 

 especially to the proximal portion of the column, while in the pre- 

 sent form they are in the distal portion, seemed to stand in the 

 way of this and it seemed preferable to place it under Gyrostoma. 



Genus Parantheopsis n, g, 



Adiniidae without acrorhagi but with conspicuous Verrucae in 

 the distal portion of the column; no collar, but the margin a distinct 

 parapet within which is a well marked fosse ; tentacles of moderate 

 length and rather slender, capable of being concealed in contraction ; 

 sphincter diifuse. 



