165 
of this sort with indifferent holes as the other trochites, but such are 
commonly pointed at their ends, and not carried out with an oval 
round as the others. There are some single joints, which are shaped 
with a double oval, that is, the oval in the upper part of them stands 
clean contrary to the oval in their lower part. In some again, the 
ovals do not stand extremely opposite to each other, but only the oval 
in the upper part of the trochite seems a little wrested from the 
direct line of the oval in the lower part, so that they stand bend-ways 
to each other, like a St. Andrew’s cross ; and there are entrochi made 
up after this manner; and I find most of the oval entrochi grow 
crooked and twisting. There are of these oval kinds of all degrees 
of tiiickness and thinness in their joints, as are found in the round 
ones, and so for the bigness of their circumference, their smoothness 
in their outward circle, and their roughness with ridges, knots, and 
branches, the length of the entrochi, their injuries, &c.” The speci- 
mens delineated at Fig. 32, 40, and 41, will illustrate the foregoing- 
remarks. 
I believe the difference of colour, observable in different trochite, 
almost always depends on the nature and quantity of any impreg- 
nation with which they may have been pervaded, whilst acquiring a 
lapideous state. Their general colour is white ; but from different 
degrees of ferruginous impregnations, they pass from a yellowish white 
to a pretty full yellow colour. They are also sometimes of a greyish 
blue ; and, according to M. Schulz, of a greenish colour. One 
species in particular, I have frequently seen of a reddish brown, and 
Mr. Walch speaks of some as being sometimes of a pale red. With 
respect to these Mr. Walch remarks that, when they possess a red tinge, 
which their matrix does not partake of, we may have some right to 
suspect that it may be the remains of the colour of the recent 
animal ; since, he observes, there are jointed sea-stars of a red colour : 
in this opinion I am disposed to concur, from what I have observed in 
one particular mass of these substances. Mr. Walch, however, will 
