In several trochitae, projecting points are observable on their sides : 

 some of these , appear to have been intended chiefly for ornament : 

 such appear to be the five regularly disposed processes on the trochites 

 at Fig. 27, which, from their regular position, almost give to the tro- 

 chites a pentagonal form. The entrochus, Fig. 7, is of a very peculiar 

 form. It is composed of plain trochitae, alternating with sharp-ridged 

 and with knobbed trochitae of a larger diameter. This specimen is 

 not in that state of perfection to allow of its being determined, whe- 

 ther or not the knobbed processes have served the purpose of articu- 

 lation with any other bodies, which have gone off laterally ; a circum- 

 stance which is rendered very probable, by the regularity of their 

 form, and disposition. It is to trochitae of this species that Mons. 

 Davila gives the name of Trochites epineuses, and to the minuter 

 points of which Rosinus applies the term Aculei minimi. 



The entrochi, Fig, 4, 9> 45, 46, have also lateral processes. In 

 these sufficient marks are. discoverable, by which it may be determined, 

 that these have been certainly for the purpose of articulation. Thus, 

 for instance, by the aid of the lens it is discovered, that the lateral 

 process of the trochites, Fig. 4, is not only a regular concavity, with a 

 crenated margin, but that there is also, in the middle of the cavity, a 

 swiall canal, which pierces through the body of the trochites, and 

 passes into the common central cavity of the chain of trochites, or 

 spinal canal. By this is shewn, not merely that this was an articulating 

 surface, but that a due communication was here also preserved with 

 the general organ of sense and of motion. 



Fig. 45 represents an entrochus which is very interesting* On the 

 uppermost of the trochitse which compose it, three of these articulat- 

 ing processes are observable : a minute trochites is also discoverable on 

 two of these processes, beiag the first of the new or second series of 

 trochitae, N 



The distorted column, Fig. 9, presents us with a set of trochitae 

 which are ornamented by small projections on their sides. These- 



