80 



GEODIA ATAXASTRA. 



The seven specimens of var. angustana (Plate 44, fig. 25) are attached to a 

 stone and partly joined. The smallest are quite regularly spherical, the larger 

 ones more irregular, elongated, divided into lobes, or tuberous. The largest, 

 which is tuberous, measures 44X41 X29 mm. Two, which are elongated, have 

 a length of 46 and 50 mm. The others are spherical or tuberous and 17-37 mm. 

 in maximum diameter. The branch-like lobes of the lobate specimens are 8-11 

 mm. broad. Except in the sheltered places adjacent to the base of attachment, 

 where remnants of a spicule-fur can be detected, the surface is bare. In the 

 smaller specimens it is almost continuous, in the larger undulating. At one 

 place on the surface of the largest specimen (Plate 44, fig. 25, right above) there 

 is a row of five low warts. Apart from these warts and the most prominent 

 convexities of the larger specimens the whole of the surface is occupied by pore- 

 sieves. The dermal membrane is, probably in consequence of post lyiortem 

 shrinkage, more or less depressed over the radial cortical canals and their distal 

 branches, so that the surface appears more or less pitted. In a restricted area, 

 6-10 mm. in maximum diameter, which is in the larger specimens situated in a 

 concavity, the dermal pores are rather large, everywhere else they are quite 

 small. I consider the small pores, which occupy by far the greater part of the 

 surface, as the afferents, the large ones, confined to the restricted areas mentioned, 

 as the efferents. 



The single specimen of var. latana is fragmentary. It has the shape of a 

 disc and measures 23X19X9 mm. Its contour is pear shaped, and it was at- 

 tached to a stone. The natural surface is destitute of a spicule-fur, quite smooth, 

 and occupied throughout by small, apparently afferent pores. 



The colour of the specimens of var. angustana is, in spirit, nearly white 

 throughout; one has a slight lilac-gray tinge. The specimen of var. latana is 

 gray with a lilac tinge throughout. 



The superficial part of the body forms a cortex, which consists of a thin, in 

 many places hardly perceptible, outer dermal layer; a middle sterraster-armour 

 layer (Plate 43, fig. 25a; Plate 44, fig. 26a), for the most part 400-700 /i thick; 

 and a thin, inconspicuous inner fibrous layer. In one place, where a foreign 

 body appears formerly to have been attached to the surface (Plate 43, fig. 25a, 

 to the left), the sterraster-armour is only 150-250 thick. 



Canal-system. More or less stellate groups of afferent pores (Plate 43, 

 fig. 26) occupy the largest part of the surface. These sieve-like pore-groups are 

 250-500 n in diameter and quite close together, their centres being only 300- 

 600 jj. apart. The pores themselves are oval or circular, 10-50 /x wide, and 



