750 PROF. A. BENDY AND MR. R. W. H. ROW ON 



Family 7. HETEEOPIID^ Dendy [1892 B]. 



Diagnosis. With a distinct and continuons dermal cortex covering 

 over the chamber-layer and pierced by inhalant pores. 

 Subgastral sagittal and subdermal pseudosagittal radiates 

 are present. Flagellate chambers varying from elongated 

 and radially arranged to sphei-ical and irregularly scattei'ed. 

 "With or without an articulate tubar skeleton. Nuclei of 

 collared cells probably always apical. 



This family is identical in scope with the family as oi'iginally 

 proposed by Dendy [1892 B], and the diftei*ence now made in the 

 diagnosis is due to the fact that our conception of the subdermal 

 triradiates has changed. Up to the present we have considered 

 the characteristic subdermal spicules in this family as being truly 

 sagittal, with the basal ray centripetally directed. We have now 

 convinced ourselves, however, by a careful examination of a 

 number of species, that this is not the case, but that the 

 inwardly pointing ray is really one of the oral rays, and that 

 the oi-iginal basal ray has taken on the appearance and position 

 of an oral ray. In other words, we find the clearest evidence 

 that these spicules are derived from ordinary distally situated 

 triradiates of the articulate tubar skeleton, which have undergone 

 rotation followed by the acquisition of a secondary pseudo- 

 symmetry. We therefore propose for them the name of 

 pseudosagittal. It will be remembered that Polejaeft' [1883] 

 recognised, in the case of Grantessa (Amphoriscus) p)ocidum and 

 G. jiamma, that the subdermal triradiates are not ordinary 

 sagittal spicules and that the centripetal ray is really one of the 

 lateral (=oral) rays and not the basal ray. He, however, con- 

 sidered that they are trira^diates of the dermal cortex which 

 have undergone re-orientation, and not, as we maintain, tubar 

 triradiates. 



Various species of the genus Grantessa show quite clearly how 

 the change has taken place. In Grantessa hirsuta we have a 

 primitive type with long chambers and an articulate skeleton of 

 many joints. At the distal ends of the chambers are tufts of 

 oxea, towards which the basal rays of the triradiates of the distal 

 joint of the tubar skeleton are inclined, as indeed occurs also in 

 the genera Sycon and Grantia. Moreover, the whole spicule has 

 become tilted until in some cases one of the original oral rays has 

 assumed a position at right angles to the surface, while the other 

 has come to lie nearly parallel to the surface, where it probably 

 serves to guard the entrance to the inhalant canal. In more 

 advanced cases, such as Grantessa sacca and G. hispida, the great 

 elongation of the now inwardly directed oral ray increases the 

 resemblance to an ordinary sagittal spicule, but a characteristic 

 asymmetiy of the outwardly dii"ected (apparent oral) rays, 

 accompanied by a definite kink or angulation in one of them, 



