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



6. Semantis spinescens, Haeckel. 



StephanoUtliis spinescens, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Bei'lin, p. IGO, Taf. 



i. fig. 29. 

 Steplianolithis spmescens, Biitschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 497, Taf. xxsii. 



figs, la, 7b. 



Sagittal ring ovate, with four pairs of thin, irregularly branched spines, two apical jsairs, one 

 on the straight dorsal rod, and one on the curved ventral rod. Basilar rod with a posterior and 

 an anterior forked rod (commencing caudal and sternal foot). Basal ring square, with two lateral 

 spines, and two triangular gates scarcely one-third as broad as the ring-gate. An internal ascend- 

 ing procolumna (rod Cj in the figure of Biitschli) connects the basal and ventral rods of the 

 sagittal ring. 



Dimensions. — Height of the sagittal ring O'l, breadth 0"07. 



Habitat. — Fossil in Barbados. 



Genus 408. Semantrum,^ n. gen. 



Definition. — S emantida witli four basal pores (two anterior jugular and two 

 posterior cardinal pores), without typical basal feet. 



The genus Semantrum, one of the most important of the Nassellaeia, arises from 

 the preceding Semantis by duplication of the two basal gates. Behind the pair of 

 coracal rods there arises from the basilar rod of the sagittal ring a third pair of lateral 

 horizontal branches, the scapular rods. These become connected with the coracal rods 

 on each side, and so produce a second posterior pair of basal pores, the " cardinal 

 gates." These are constantly larger than the anterior "jugular gates." Therefore the 

 vertical ring of Semantrum possesses a horizontal basal ring with four very characteristic 

 gates, enclosed by three pairs of lateral curved and connected iDranches, and these 

 become transmitted by heredity to the majority of the Nassellaeia. 



1. Semantrum quadrifore, n. sp. (PI. 92, fig. 5). 



Sagittal ring subcircular or ovate, with three edges and four sagittal forked spines on the odd 

 edge (two dorsal and two ventral spines). Basal ring decagonal, with ten simple or forked spines 

 on the ten corners. Jugular gates tetragonal. Cardinal gates pentagonal. 



Dimensions. — Height of the sagittal ring 0'09, breadth 0-07. 



Habitat. — Tropical Atlantic, Station 351, surface. 



^ iS'eniawfrMm= Signet-ring; aifiavr^oii. 



