562 Transactions of the Society. 



instance (Fig. 4*), the axial canal is enlarged close to the point, 

 and it opens widely with a very thin cylinder of silica around it. 

 Then it narrows to the normal size, and again enlarges so as 

 almost to fill up the rest of the spicule, bulb included. There is the 

 veriest shell of solid matter surrounding it. Other specimens show 

 uniform enlargement of the axial canal and of its usual globular 

 ending, the dimensions being from just beyond the normal to 

 almost complete filling up (Fig. 4a). The enlargement in the bulb 

 is often irregular in shape. 



(2) Enlargement with perforating tubules reaching the axial 

 canal from the exterior (Fig. 4&). The sides of the axial canal, 

 where penetrated by the minute tubules from without, present a 

 rotten appearance, the outline is ragged, and erosion seems to be 

 going on irregularly, from within outwards. Higher up, the canal 

 is normal, but at the basal termination there is a long and somewhat 

 irregular swelling. 



(3) In another specimen, numerous perforations occur in the 

 bulb and several in the stem, and some reach the axial canal, which 

 is regularly and symmetrically dilated, or simply enlarged in its 

 calibre. This appears to be the commonest type of departure from 

 the normal condition of the axial canal (Fig. 4c). The perforations, 

 when seen from above, show circular disks differing in their light- 

 transmitting power from the rest of the spicule, and when seen side- 

 ways are very small sections of cylinders, hollow and about the 

 breadth of a normal axial canal, but sometimes they are larger 

 (Fig. id). 



There are some acuate spicula in the deposit, rounded at one 

 end, attenuate at the other, slightly bent or straight, and they 

 present several modifications of the axial canal, which normally is 

 very linear and equal in its calibre. 



A slightly bent form (Fig. 5a), about t-qVo ii^ch in breadth 

 at the larger end, has the axial canal slightly open at the end, 

 and there is an enlargement of its calibre, which is rounded and 

 greatest close to the larger termination. In another specimen, 

 the canal, open at the small end, does not widen for some distance ; 

 but then it enlarges gradually and has its calibre so increased that 

 the axial canal can be recognized as a tube nearly filling the whole 

 of the remainder of the spicule (Fig. 5h). 



There is the top of a large acuate spicule in one of the prepa- 

 rations, which has become fractured in consequence of thinning, 

 owing to a great development of the axial canal. The tip of the 

 spicule (Fig. 5c) has an open axial canal slightly enlarged, which 

 increases in size in the form of a reversed cone with wavy margins, 

 until a cylindrical expansion is produced nearly filhng the body. 

 The parietes became so thin that after fracture but a layer of sihca 

 remained to indicate the position of the former nearly solid spicule. 



