32 
thence into the funnel-shaped cavity. This has suggested to me the idea that 
it might have led to an ovary having five ducts, somewhat similar to that of the 
echinus. | 
Externally the superiór portions of this animal are frequently marked with 
minute indentations (Pr. 1. fig. 2.) the points of adhesion probably of the epider- 
mis, or rather periosteum, which secreted their calcareous matter. In sorrie in- 
stances I believe I have detected traces of this epidermis in a fine overlaying 
pelicle. 
Ifthe periosteum of any single joint received an injury, the further secre- 
tion in that part was discontinued, and the periosteum of the neighbouring 
parts filled the vacancy thus occasioned ; this produced a wedge-like interpo- 
sition and deformity of the joints of the column, which thereby appear as 
if formed of several parts; a similar distortion of the pelvis, &c.—Pu. vir. 
fig. 1. to 6. 8. to 10. 
/ 
Although the whole skeleton of the animal is now changed into calcareous 
spar, still, as has been observed, the difference of colour not unfrequently points 
out the gradual formation of its various parts: hence we may, perhaps, reason- 
ably conclude that the original colouring matter has been retained through all 
. the changes the substance underwent. In fine specimens this is a beautiful dark 
purple, varying in a most elegant manner into a pale red purple, and to a more 
or less dark gray, as may more particularly be seen in sections of the base. 
These colours, however, appear only to have been retained in those speci- 
. mens which either were, or had very recently been, living at the period of their 
becoming enveloped in the strata which now preserves them. Those which 
had been at that period dead for some time, must have already from various 
evident causes, lost much of the vividness of the original colours before they 
were thus inhumed. This appears to me to have been the case with those 
specimens which so frequently occur, having an uniform gray colour, becoming 
tinged by further dec omposition with yellow, and gradually converted into a 
kind of ochre, i 
_ The calcareous particles which have filtered into the alimentary canal and 
the various cavities between the joints (if these were free of extraneous matter) 
often form there a nucleus of foliated spar, and sometimes occur as casts 
