1'LACOÖOMA l'AUAt)tCTYUM. lo 



The dermalia and tlic gastralia are likewise spicules whose shape 

 and size present points of approach to the parenchymal hexactins. 



The dermalia are hexactins, in part somewhat sword-like in 

 shape as in the generality of the Euplectellid members, but in 

 part much flattened owing to an extensive shortening of the 

 proximally directed blade-ray. In details of characters they differ 

 somewhat according as they are located on the front or on the 

 back of the sponge-body. 



First, the dermalia of the frontal lattice (PL II., figs. 1 and 

 2). The rays measure about 9,« in breadth near the spicular 

 center. The distal free ray is ahvays very short, being only A')- 

 ÖÖ I'- and seldom 'do <)■ in length ; it usually broadens slightly 

 towards the distal end, which is rounded and has a surface 

 supplied with quite insignificant microtubercles. The paratangen- 

 tial rays are 150-200/^ long, as measured from the center; they 

 taper outwards in a l)arely perceptible degree, to terminate with 

 rounded or bluntly conical tips ; the surface is sprinkled with 

 obsolete microtubercles which are distributed more densely near 

 the end of the rays. The proximally directed ray resembles the 

 paratangential s in general appearance but is subject to great 

 variation as to its length, according to the position of the dei'malia 

 in the frontal lattice. Where there exists a liy^Dodermal beam 

 directly underlying the dermal layer, the spicules of the latter 

 have a more or less elongated proximal I'ay dipping right into 

 the substance of the former. That ray is then considerably — at 

 times even thrice — longer tluin a paratangential of the same 

 spicule (PI. II., fig. 1). Whereas, within a mesh-area bounded 

 by hypodermal beams, i. e., in parts where the dermal layer has 

 no skeletal support underneath, the dermalia have their proximal 



