1084 THE VOYAGE OF H.M.S. CHALLENGER. 



3. Pylospyris canariensis, n. sp. (PI. 95, fig. 16). 



Shell rough, with deep coronal and slight sagittal constriction. Galea hemispherical, with 

 numerous small irregular, roundish pores, about half as long as the cephalis, with a slender conical 

 horn of twice the length. Cephalis nut-shaped, with larger roundish pores of very unequal size, 

 three pairs of larger pores on each side of the ring. Basal plate with two larger pores. 



Dimensions. — Galea 0'03 long, 0'08 broad; cephalis 0-06 long, O'll broad. 



Habitat. — North Atlantic, Canary Islands, surface. 



Family LIV. Phormospyrida, Haeckel (sensu emendato) {PL 83, figs. 13-15 ; 



PL 95, figs. 17-19). 

 Phormospyrida, Haeckel, 1881, Prodromus, p. 442. 



Definition. — S pyroidea with a thorax, without galea; the shell composed of the 

 bUocular cephalis and of a simple thorax arising from its basal face. 



The family Phormospyrida differs from the Zygospyrida, their ancestral group, 

 in the development of a thorax, or a second fenestrated shell-joint, which arises from the 

 lower face of the cephalis. It corresponds, therefore, to the Dicyrtida among the 

 Cyrtoidea, and may perhaps be, wholly or partially, the ancestral group of the latter. 

 When the sagittal ring and the longitudinal constriction of the cephalis disappear, 

 the Phormospyrida pass over into the Dicyrtida. 



Only three species of this famUy have been hitherto known, which were found fossil 

 in Barbados, and described by Ehrenberg (1875) as Lithohotrys stiligera and Petalosjyyi-is 

 conjiuens, and by Biitschli (1882) as Petalospyris anthocyrtoides. Fifteen other species 

 are found in the Challenger collection, which we dispose here among five genera. 



Two of these five genera (the horned Acrospyris and the hornless Phormospyris) 

 possess the three typical basal feet of Cortina and Tripospyris, and may be derived 

 from these genera by the development of network between the bases of the feet. The 

 three other genera possess numerous feet, and may be derived in the same way from 

 the Polyspyrida; the apical face diff"ers in the three genera, in Desmospyris it is 

 hornless, in Patagospyris it bears an apical horn, and in Rhodospyris three horns 

 (an apical and two lateral or frontal). 



The cephalis in the Phormospyrida exhibits the same typical structure, which we 

 have described above, of all Spyroidea (compare, p. 1017). The thorax or the second 

 joint of the shell arises by reticular connection of the bases of the basal feet, and 

 represents a cylindrical or truncate-conical joint in the polypodal forms, or a three-sided 

 joint in the tripodal forms. The terminal aperture or the mouth of the thorax is 

 constantly open, and surrounded by the free ends of the feet. 



