384 Mr. H. J. Carter on the " Tuhulations Sahleuses " 



Central cylinder. — This, which is structureless and com- 

 posed of quartz-sand more or less agglutinated together by 

 semicrystallization into the form of quartzite, may be circular 

 (fig. 7, a) or oval (fig. 8, a) in the transverse section, thus 

 indicating its general shape in this respect. The largest frag- 

 ment of the former that I possess, when extricated from the 

 tuberculous crust, is 10 centims. long and 8 millims. in 

 diameter throughout, so that there is no diminution in size 

 from one end to the other (fig. 5) ; and each end having been 

 truncated by fracture in this as well as in all the other frag- 

 ments sent to me (which so far are alike), shows that none of 

 them possess the natural extremities of this form, which, from 

 what has been premised, in the typical specimen, as well as 

 that which will be presently mentioned, shows at least that, 

 in its natural state, one end is reduced to a point. The sur- 

 face of the circular form presents a trapezoidal or quadrangular 

 subcircular reticulation of grooves, which surrounds the cylin- 

 der and in the most perfectly formed portions has a scaly 

 appearance, in which the interstices are equal, having two 

 angles opposite and longitudinal, and the other two opposite 

 and transverse, with a distance of 7 millims. between each of 

 the " two angles " and a convex area respectively (fig. 5, a). 

 With the exception of this form varying in diameter with age, 

 I can state no more of it. Not so, however, with the oval or 

 compressed form, which is lobed or segmented longitudinally, 

 18 centims. long and 8 by 15 millims. in transverse diameter 

 (at least such are the dimensions of my best specimen, 

 fig. 2, c c) ; for although truncated by fracture above like the 

 rest (fig. 2, d), it terminates below or behind in a naturally 

 pointed extremity (fig. 2, e), and presents throughout its 

 whole length a linear central groove (fig. 2, g) , from the 

 anterior portion of which (in fig. ^,ff) the remains of several 

 smaller grooves in succession, at equal distances of about a 

 centimetre each, may be seen extending outwards, backwards, 

 and downwards, resembling altogether, in position and direc- 

 tion, the dorsal vessel and its lateral branches in an Annelid, 

 unless the latter be likened to the grooves between the seg- 

 ments. 



Branched form. — In another specimen of the same length 

 but of the " circular " form, truncated by fracture at each end, 

 and irregularly sigmoid in its general course (fig. 4, cc), four 

 similar cylinders branch off from the main one in different 

 directions and apparently from different and opposite parts of 

 the main cylinder, each of which terminates, after curving 

 outwards for a distance of 3 centims., in an abrupt end 

 also truncated by fracture, but rather of a compressed or oval 



