914 THE VOYAGE OF H.M.S. CHALLENGER. 



2. Plagonidium quadrigeminum, n. sp. 



Spines cylindrical, curved, eight to ten times as long as the common central rod, in the distal 

 half forked ; the fork -branches curved, somewhat longer than the basal part. 

 Dimensions. Length of the spines 018, of the middle rod 0'02. 

 Habitat. Antarctic Ocean, Kerguelen Island, Station 159, surface. 



Genus 389. Plagiocarpa, 1 Haeckel, 1881, Prodromus, p. 424. 



Definition. P lagonida with four unequal radial spines, arising in pairs from 

 the two poles of a common central rod ; one ascending apical spine opposed to three 

 descending basal spines. 



The genus Plagiocarpa agrees with the preceding Plagonidium in the possession 

 of a common horizontal middle rod, the two poles of which bear two pairs of divergent 

 spines; but whilst in the preceding all four spines are equal, here they are differentiated 

 in the same manner as in Plagoniscus, which differs only in the absence of the middle 

 rod. The two observed and closely allied species of this genus are of peculiar interest, 

 since they belong possibly to the common ancestral forms of the NASSELLAEIA ; the 

 basal middle rod corresponds perhaps to the basal part of a sagittal ring, the apical 

 spine to its dorsal part, the three other spines to the basal feet (compare above, p. 902). 



1. Plagiocarpa procortina, n. sp. (PI. 91, fig. 5). 



Spines cylindrical, curved, thorny, three to four times as long as the common middle rod. 

 Apical spine and the meeting caudal spine (or the posterior basal spine) somewhat larger and with 

 more numerous thorns than the two paired pectoral (or anterior) spines. From the common base 

 of the latter arises an anterior prolongation of the horizontal middle rod, which m the sagittal plane 

 is curved upwards and corresponds to the sternal foot of many Cyrtellaria. An ascending 

 branch of this spine is opposed to a descending branch of the apical spine, both together forming an 

 incomplete sagittal ring. 



Dimensions. Length of the two larger spines 0'15, of the two smaller 0'12. 



Habitat. Mediterranean (Portofino near Genoa), surface. 



2. Plagiocarpa procyrtella, n. sp. 



Spines of form and arrangement similar to those of the preceding species, but longer and more 



branched, six to eight times as long as the shorter common middle rod. The two characteristic 



1 Plagiocarpa = Having its fruit (the central capsule) on the side ; 



