246 



Tubulär, unbranched, closed at tbe extremity. 



Euplectella cucumer. 



Lithistidae. Spicules developed upon a quadriradiate divi- 

 sion of a central canal, held together by amorphous sarcode and an 

 interlocking of their filigreed arms, forming a reticulated glassy 

 structure, whose interspaces are more or less irregulär and curvi- 

 lincar. Composed of two kinds of skeleton - spicules, those which 

 form a layer on the surface and are companied by minute or flesh- 

 spicules characterising the species, and those forniiug the body, which 

 are more or less alike in all the species and accompanied by fewer 

 flesh-spicules. 



a. Species in which the surface-spicule consists of a shaft and 

 three straight bifurcated arms all smooth and pointed. 



Dactylocalyx Bowerbankii, D- Masoni, Corallistes typus. 



b. The three sinuous arms branched. 

 Theonella, Dactylocalyx Prattii. 



c. The three sinuous arms compressed verticaily; branched aud 

 dentate or curvilinear on the margins. 



Mac-Audrewia, Corallistes clavatella, Kaliaspis. 



d. The surface-spicule consists of a ahort shaft and subcircular 

 discoid head, deeply and irregularly fissured. 



Corallistes polydiscus. 



e. The surface-spicule consists of a short shaft and subcircular 

 discoid head. 



Dactylocalyx polydiscus. 



f. The three arms of the surface • spicule sinuous, branched, 

 curvilinear, tubercled on the upper side or outer aspect, and fili- 

 greed at the extremities; shaft filigreed also at its extremity. 



Äzorica Pfeijferae n. sp. Madeira. 



g. The surface-spicule is much the same, but with others like 

 those of Dactylocalyx Bowerbankii and D. polydiscus among the 

 body -spicules. 



Corallistes borealis n. sp. Faroe. 



h. The surface-spicule consists of a long shaft and three arms, 

 bifurcated and more or less tuberculated on the outer or upper aspect. 



Corallistes noli tangere. 



i. Surface-spicule like that of Dactylocalyx Masoni, with the 

 branches of the body-spicules in like manner glomeratu-tubercled. 



Corallistes microtuberculatus. 



k. Surface spicule like that of Dactylocalyx Bowerbankii ; the 

 rest with large filigreed head and long sinuous shaft filigreed at 

 the extremity. 



Corallistes elegantior, 



1. Species with curly filigreed spicules. 



