70 
ORGANIC DEPENDENCE AND DISEASE 
described in manuscript , 1 taken from the Onondaga lime- 
stone of New York. It is like Megistocrinus in its general 
form with a broad upper surface or tegmen and very large 
aboral opening. Our illustration shows a specimen of this 
crinoid with the scar of at- 
tachment made by a shell 
which became fixed early and 
clung to its situs throughout 
life, the enlarging scar grow- 
ing eccentrically from the 
anal aperture, and leaving a 
deep sinus about the bulging 
adjoining portions of the 
growing crinoid. 
In the Middle Devonian 
Hamilton shales of Tlied- 
ford and Bosanquet, Ontario, 
occurs the platycrinid spe- 
cies Hystricrinus carpenteri 
Hinde, a peculiar genus with 
surface spines jointed to the 
calyx by a ball-and-socket arrangement. The species 
is known only in the shales of these localities. Two 
species of gastropods have been found attached to the 
aboral surface and dome; one a smooth form, Platyceras 
erectum Hall, and the other a spiny shell which has been 
incorrectly called P. dumosum Hall. These shells have 
not been found attached to any other crinoid and no 
other crinoid of the Hamilton shales in that vicinity has 
thus far shown evidence of such combination. This com- 
bination is thus closely restricted locally. The crinoid with 
its broad tegmen or vault, diffuse arms and absence of anal 
proboscis, offers every convenience for this adjustment, but 
i By Winifred Goldring in preparation of a Monograph of the New York 
Devonian Crinoidea. 
Fig. 56. Upper surface or dome of 
crinoid (Craterocrinus) with anal 
opening and scar of shell attach- 
ment. Devonian. 
