204 PROF. OWEN ON EUPLECTELLA. 



fibres, in like manner, are resolved at the truncated apex of the cone into their com- 

 ponent filaments, which intersect those proceeding from the longitudinal fibres, as well 

 as similar pencils from the oblique fibres, the whole forming an irregular silky tuft 

 which almost closes the apical aperture of the cone. 



The longitudinal fibres are external to the transverse ones, to which they are con- 

 nected by both the spiral fibres and by smaller and less regular intersecting fibres at 

 the angles of the squares ; the area of each square is thus reduced more or less to a cir- 

 cular form". At about one or two inches from the apex these connecting reticulate fibres 

 begin to rise in the form of narrow ridges from the general surface of the network, and 

 nearer the apex on the convex than on the concave side of the bent cone : these ridges at 

 first are short and interrupted ; they are then more extended but irregular in their course, 

 some being transverse, others undulated or curved ; but as they approach the base of the 

 cone they are continued into broader ridges, which follow with more or less regularity 

 the course of the obUque spiral fibres ; the broadest of these ridges measures two 

 lines and a half: their structure presents an extremely fine and irregular network, dis- 

 posed for the most part in two plates, which converge as they recede from the general 

 wall of the cone, and coalesce in a sharp and well-defined edge. The component fibres 

 of these reticulations, like those of the main network, are resolved into the fine silky 

 filaments above mentioned : the fibres of the coarse irregular network which closes the 

 basal aperture of the cone, and which constitutes the main characteristic of this Alcyo- 

 noid sponge, appear to be directly continued from, and, as it were, to include all those 

 which enter into the composition of the longitudinal transverse and oblique fibres of the 

 wall of the cone ; the frill-hke ridge above mentioned defining the line of transition from 

 the one to the other. The inner surface of the reticulate parietes of the cone is even ; 

 not interrupted by any ridges or processes like those on the outer surface. 



The number of the longitudinal fibres at the base of the cone is sixty ; that at the 

 smaller end, where they begin to resolve themselves into their constituent filaments, is 

 thirty : the diameter of the longitudinal fibres is about one-fortieth of an inch ; that of 

 the transverse fibres is somev;hat less : the oblique fibres, where they are most regular, 

 average one-sixtieth of an inch ; the longitudinal fibres, where they begin to resolve 

 themselves into their component filamentg, expand in the direction of a line passing to 

 the centre of the cone, and not in the direction of the plane of its circumference, main- 

 taining, in the latter respect, nearly the same breadth to their entire unravehng; 

 whilst in the other dimension they equal one line in breadth before they are wholly 

 decomposed. 



Small portions of a finely reticulate plate were loosely attached to some parts of the 

 internal surface of the cone : the fibres of these pieces consisted of minute filaments, 

 irregular in their course, branching, anastomosing, and sending off" abrupt processes like 

 thorns. 



' PI. XIII. 6?. 4. 



