The Genus Porosphop/ra, Steinmann. By George J. Hindc. 25 



skeleton consist of four-rayed spicules, in which one ray is taper- 

 ing and the other three blunted and organically fused to adjoining 

 spicules. They also possessed originally a crust or dermal layer 

 of smaller spicules than those of the skeletal mesh, which are 

 not fused together, and also in some forms a distinct spicular base 

 is present. In the form of the skeletal spicules and in their 

 arrangement Porosphcera closely resembles the Calcisponge genus 

 Plectroninia, Hinde, from the Eocene (?) Tertiary of Australia, and 

 the recent Petrostroma, Doderlein, from the Japanese sea, and with 

 these genera it finds a place in the Lithonina group of Calcisponges. 

 Descriptions are given of the following species : P. globularis, 

 Phill., P. nuciformis, von Hag., P. Woodicardi, Carter, P. pileolus, 

 P. patelliformis, sp. n., and P. arrecta, sp. n. 



