Mr. H. J. Carter on the Polytremata. 207 



of tlie cavities, originally in the interior, had become filled with 

 calcspar ; and the rest were empty. When entire, the whole 

 consisted of a spheroidal mass of reticulated structure, with 

 rough papillated exterior, traversed by a large axial space in 

 the form of an elongated cone, whose point, situated close to 

 the circumference on one, extended to the base which occupied 

 a portion of the circumference of the other side. This elon- 

 gated cone, which attains in the centre a diameter of one third 

 of an inch, and presents an irregularly scalloped line on the 

 surface in the section, diminishes slightly towards the base, 

 and is surrounded on all sides, except the extremities, by con- 

 centric layers of chambers ("chamberlets," Carpenter, Phil. 

 Trans. 1869, vol. clix. pt. 2, p. 728), also excavated in the 

 reticulated structure, each chamber being more or less irre- 

 gularly quadrangular, representing in miniature a ayjjt arising 

 from four columns, whose pillars and arches are formed by the 

 reticulated structure ; w^hile all the chambers or "crypts," being 

 piled one upon another in radiating columns, undergo division 

 successively as they extend outwards from the cone, so as to fill 

 the spaces that would otherwise be left towards the circum- 

 ference, since the chambers, although very irregular in shape, 

 are much the same in size throughout. Hence, when a longi- 

 tudinal section is made through the centre of the conical space, 

 the reticulated structure is also observed to be in radiating 

 columns, which present a series of floral-like expansions as 

 they successively follow each other in forming the columns 

 of support to the arches of the cryptiform chambers re- 

 spectively. 



As there is an irregularly reticulated structure, so there 

 must be the same form or kind of continuous interstices ,• and 

 this has been termed by Dr. Carpenter the " labyrinthic system " 

 {torn. cit. p. 729) ; besides which, this labyrinthic system 

 opens into larger spaces of a short cylindrical form, which 

 chiefly occupy the pillars of the crypt-like chambers, and thus 

 possess a more or less radial direction, although they are by 

 no means more continuous or regular in position than those of 

 Polytrema mimaceum above mentioned. These are the " radi- 

 ating tubes " of Dr. Carpenter {torn. cit. p. 728). 



In consequence of the axial conical space in my specimen 

 being distinguished from the rest of the structure by the pre- 

 sence of a heterogeneous mass of foreign material, among 

 which may be observed innumerable fragments of sponge- 

 spicules and minute Foraminifera, while this is limited in one 

 direction by the closed conical end, and continued to the sur- 

 face of the test at the other or basal extremity of the axial 

 space, it seems that the latter was the direction of the main 



