70 



ORGANIC DEPENDENCE AND DISEASE 



described in manuscript/ 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 Thed- 

 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 



Fig. 56. Upper surface or dome of 

 crinoid (Craterocrinus) with anal 

 opening and scar of shell attach- 

 ment. Devonian. 



1 By Winifred Goldring in preparation of a Monograph of the New York 

 Devonian Crinoidea. 



