84 THE SPONGES. 



branches is 10-20 mm. The .ixial cavity is large as compared with the 

 thickness of the wall. For instance, in a branch 20 mm. wide, the width 



of the axial cavity is 10 mm. The skeletal reticular plates are about 



2 mm. apart. At the dermal surface they are abundantly connected by 

 anastomoses so as to produce a reticulum with rounded polygonal meshes 

 about 2 mm. in diameter, agreeing in this respect with the specimens 

 described by Schulze (1887, p. 329). 



Hexadinella tubuhsa F. E. Sch. has hitherto been recorded only from 

 Japan. 



Sclerothamnopsis compressa, gen. et sp. nov. 



Plate 9, Figs. 2, 4, 6-8, 10, 11 ; Plate 10, Figs. 1, 3. 



Diagnosis. Dictyonal framework a close reticulum not divisible into lamellae. Beams 

 of the reticulum may give rise to fibres, which pursue a longitudinal course in places, 

 curving outward to the surface. The entire framework lias the shape of a branching axis. 

 The main axis and the branches all lie approximately in one plane, and all are distinctly 

 flattened. Free spicules not known with certainty. 



At Station SJfiG five fragmentary and macerated specimens were taken 

 of this remarkable sponge, which finds its nearest ally in Sderothamnus claiisii 

 Marshall. The most perfect piece is represented in Fig. 1, Plate 10. 



The body of the skeleton consists of a branching axis, which is not 

 cylindrical, but distinctly flattened. From the flattened surfaces of the 

 axis the branches project obliquely upward, some of them reuniting with 

 the axis above. The branches and the main axis all lie approximately in 

 one plane, the whole sponge (fragment) thus acquiring a habitus, which 

 is not bushy but flattened. The branches themselves are flattened and 

 like the axis in planes vertical to that in which the sponge body spreads. 

 The branches vary in size, some being nearly as thick as the axis, others 

 thin and small. Neither the base nor the upper end of the sponge is 

 included in the specimens, the largest of which measures 150 mm. in 

 length, the transverse diameters of the axis being about 10 mm. and 

 20 mm. 



The macerated skeleton appears as a dense stony mass, the surface of 

 which is studded with the round apertures, mostly about 0.5 mm. in diam- 

 eter, of small canals passing into the interior. Here and there cylindrical, 

 canal-like spaces of considerable size, 3 to 6 mm. in diameter, pass in an 



