. ~ "iy^Cradd. Rbuc Nsobs Text-fig. 40. Nectopyramis spinosa Sears. A, dorsal view; B, lateral view of nectophore of first type, with obsolescent nectosac, 'Scotia' 1951 Cruise, St. 363 ; C, lateral view of nectophore of second type, with functional nectosac, 'Discovery II' St. 1639. *9-5- Although there is some variation in the arrangement of spinose ridges in the first group of three nectophores with obsolescent nectosac, there are elements in their arrangement that can be compared with that in the second group of two nectophores with the larger nectosac. For instance we find the same d
. ~ "iy^Cradd. Rbuc Nsobs Text-fig. 40. Nectopyramis spinosa Sears. A, dorsal view; B, lateral view of nectophore of first type, with obsolescent nectosac, 'Scotia' 1951 Cruise, St. 363 ; C, lateral view of nectophore of second type, with functional nectosac, 'Discovery II' St. 1639. *9-5- Although there is some variation in the arrangement of spinose ridges in the first group of three nectophores with obsolescent nectosac, there are elements in their arrangement that can be compared with that in the second group of two nectophores with the larger nectosac. For instance we find the same dorsal-median and what I will call ' buccal' ridge in both groups; but more material is needed to complete the morphological account. Nectopyramis (including Archisoma) is the only Prayid genus known in which the nectophores bear ridges. We may have here, in the existence of two types of nectophore, a phenomenon similar to that found in Amphicaryon, where one nectophore has an obsolescent nectosac. This would be of special interest seeing that other species of Nectopyramis have only one nectophore as far as we know, though presumably their ancestor had more. It is possible that one type of nectophore represents a caducous larval, and the other the definitive nectophore. In favour of this interpretation is the fact that the somatocyst or pallial canal is extended well beyond the obsolescent nectosac in the first group of necto- phores. This extension is characteristic of larval Prayid nectophores. In the second group the pallial canal stops short at the ventral radial canal of the nectosac, just as it does at the pedicular canal in definitive nectophores of Prayids. Since I wrote this note Dr Mary Sears has published (1952) a note on this siphonophore, of which ' Dana' took six specimens—one with the large and five with the obsolescent nectosac. Three were taken in the Indian Ocean, two in the South Pacific and one in the Tropical Atlantic. In none of them were the stem or appe
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