1078 THE VOYAGE OF H.M.S. CHiiLENGEE. 



The number and disposition of the terminal feet around the basal plate do not vary 

 so much in the Tholospyrida as in the Zygospyrida. We find here only one genus 

 with three feet, Tholospyris (corresponding to Tripospyris) ; one genus with two 

 lateral feet, Lophospyris (corresponding to Dipospyris] ; and two genera with numerous 

 feet, the horned Sepalospyris and the hornless Tiarospyris (the former corresponding 

 to Petalospyris, the latter to Gorgospyris}. The fifth genus (Pylospyris) has no feet 

 at all, and may be derived from Circospyris among the Zygospyrida. 



The cephalis exhibits in the Tholospyrida the same typical structure which we have 

 described above of all Spyroidea (compare p. 1017). The cupola or galea, arising 

 from its upper face, seems to be a secondary production, perhaps caused by an apical 

 growth of the central capsule, or in other cases by descending branches of the apical 

 horn, which cover the apical face of the calymma with protecting network. 



Synopsis of the Genera of Tholospyrida. 



I. Subfamily \ Three basal feet (two paired pectoral and 



Lophospyrida. J an odd caudal), . . .469. Tholospyris. 



Two or three basal (cortinar feet). Galea 1 



with a horn. [ Two paired basal (pectoral) feet, . 470. Lophospyris. 



II. Subfamily 



Tiarospyrida. 



Numerous basal feet in a corona (six to nine 

 or more). 



Galea with a horn, . . .471. Sepalospyris. 



Galea without a horn, . . . 472. Tiarospyris. 



III. Subfamily ) 



Pylospyrida. / Galea with a horn, . 473. Pylospyris. 



No basal feet. 



Genus 469. Tholospyris, 1 Haeckel, 1881, Prodromus, p. 441. 

 Definition. T holospyrida with three basal feet and an apical horn. 



The genus Tholospyris is probably the common ancestral form of the Tholospyrida, 

 and has arisen from Tripospyris by development of a galea or cupola; this is composed 

 jf the apical horn, the lateral branches of which become connected with lateral spines 

 arising from the coryphal face of the cephalis, and of lattice-work developed between 

 the former and the latter. The three descending feet of the basal face are the typical 

 cortinar feet (one odd caudal and two paired pectoral), the same as in the old ancestral 

 genera Cortina, Plagoniscus, Tripospyris, &c. 



Subgenus 1. Tlwlospyrium, Haeckel. 

 Definition. Basal feet simple, neither forked nor branched. 



1 Tholospyris = Basket with a cupola ; ta'Tioj, ami^ls- 



