78 DISCOVERY REPORTS 



natans in the genus Nectopyramis, but we cannot exclude N. diomedeae, because the branches of the 



somatocyst of its polygastric stage can be homologized with those of N. thetis (see p. 84). 



A new species N. spinosa was published by Sears (1952) after this report was written. I have dealt 

 with it on p. 86. 



Nectopyramis thetis Bigelow, 1911a. 



Attention has been drawn on p. 77 to the apparent close relationship between this species and 

 Archisoma (= Nectopyramis) natans, and to its differences from Nectopyramis diomedeae. 



The eudoxids of N. thetis and N. natans each have a flattened dorsal (posterior sensu Bigelow, 

 anterior sensu Leloup) surface (Leloup, 19326, calls it 'une crete mediane'), up to which reaches 

 a small branch of the ascending canal (not shown by Leloup). But whereas there are in the eudoxid 

 of N. thetis two lateral projections of the margins of the facet, each served by a lateral (sensu 

 Leloup, transverse sensu Bigelow) canal, in N. natans both projections and lateral canals are absent. 

 But in N. pyranm also the branch of the ascending canal reaches the dorsal surface. 



C long. 



Text-fig. 35. Nectopyramis thetis. Growth stages of eudoxids and homologies of bracteal canals with those of 

 Abylids: A after Leloup, B, C, D after Bigelow. E, Abylopsis tetragona. 



The eudoxids, or stem groups, of the following Prayids are now known : Praia dubia, P. reticulata, 

 Rosacea cymbiformis, R. plicata, Maresearsia praeclara sp.n. Amphicaryon spp. indet., Nectopyramis 

 thetis, N. diomedeae and N. natans. They are all homologous, but Amphicaryon eudoxids, of which 

 Eudoxia tottoni Leloup, 1934a, is one, appear to me much more primitive in that the bract is 

 simple, helmet-shaped, and carries only a pair of longitudinal (sensu Leloup) bracteal canals running on 

 each side of the bracteal cavity. But with this difference is correlated the fact that the bracts of 

 Amphicaryon only extend on one side of the stem, whilst in all the rest of the genera they are attached 

 athwart the stem, so that the half of each bract which corresponds with the whole Amphicaryon bract 

 bears a similar pair of bracteal canals in the walls of the bracteal cavity. The ascending and descending 

 bracteal canals, absent from the Amphicaryon bract, appear to have arisen as the bract extended on to 

 both sides of the stem and increased in thickness above it. The ascending canal in each case arises 

 from one of the longitudinal canals, though not on the same side in all Prayids. Bigelow (1911a) had 



