GO THE VOYAGE OF H.M.S. CHALLENGER. 



elongated conical form, and are capable of being retracted. In some of the specimens 

 they seem to be rather inflexible, though they mostly possess a high degree of pliability* 

 this is especially the case in the individuals from Station 299. The animals from that 

 station are also distinguished by the enormous length of their processes, which being 

 about 125 mm. are nearly of the same length as the body. The processes, often brittle 

 and easily broken off, have sometimes the tops bipartite. The specimens from Stations 

 146 and 157 are provided with processes of comparatively small size. 



The perisoma is more or less strongly developed, and is sometimes pliable, sometimes 

 very hard, brittle, transparent, and clear like glass. It is strengthened by numerous 

 calcareous deposits which have the form of larger or smaller, more or less distinctly 

 circular plates (PI. XXXI. fig. 1), and are in some individuals closely crowded and overlap 

 one another, the perisoma becoming thus more solid and brittle than in other specimens, 

 where the plates be side by side at greater or smaller distances from one another. The 

 position of the calcareous deposits doubtless greatly depends upon the extent to which 

 the perisoma is contracted ; they seem usually to be more closely crowded on the dorsal 

 than on the ventral surface, though sometimes the contrary is the case. The plates do 

 not He closer than to form two layers, of which the exterior one is distinguished by the 

 smallness of its deposits. It is a remarkable fact that while some of the individuals 

 possess two layers of deposits, others have only one. The plates, varying greatly in size, 

 sometimes measuring about 2*2 mm. or more in diameter, are flat, discoidal, slightly convex 

 outwards and perforated by a great number of usually somewhat circular holes, of 

 which those at the middle are of a considerable size, attaining about 0"32 mm. in 

 diameter ; the size of the holes diminishes towards the circumference of the plates, and 

 are consequently only visible as small points round the periphery. The convex side of 

 the plates carries one or more small processes or spines situated close to or at some dis- 

 tance from the the centre ; those spines are partly simple, partly give off small branches 

 at their top, which running parallel with the plate itself are in connection with similar 

 branches from other spines, thus forming a network upon the original plate. Here and 

 there plates are found without any projections ; several of the individuals obtained at 

 Station 157 are remarkable from having all then- plates quite smooth and destitute of 

 spines. Besides the fully developed plates I have found a multitude of others in stages 

 of development. The individuals dredged at Station 157 have the plates extremely 

 firmly constructed and with comparatively small holes. 



The pedicels contain a great number of calcareous deposits (PI. XXXI. fig. 3), of almost 

 the same shape as the above-described plates, though usually smaller ; towards the ends 

 the deposits become more simple in form, consisting of longer or shorter rather straight 

 spicula or rods, the ends of which are branched or dilated and perforated. Those spicula 

 have a transverse position. The large circular sole-like end of the pedicels has, besides 

 those more important deposits, a greater number of small almost unbranched spicula, but is 



