336 
PALAEONTOLOGY OF NEW YORK. 
S. scintilla, S. Keokuk) which have usually been found attached to flatter sur¬ 
faces. 
Mr. Etheridge makes the following interesting observations on these 
fossils : 
“ When the organism to which the Productus is attached is of larger size 
than the latter, the whole of the ventral valve is applied to it, the spines 
spreading out and around on each side; but when the foreign body is of less 
diameter than the Productus, as is usually the case with fragments of Polyzoa, 
several of the spines are wound tightly round, especially near the beak, and 
the remainder of the valve remains free. Attachment took place during the 
life of the Crinoid; for in nearly every case where the Productus remains 
adhering, we find that its rate of growth was less than that of the Crinoid, the 
result being that the substance of the latter surrounded or enclosed its parasite, 
first the encircling spines disappearing and gradually the shell. We have 
specimens showing this remarkably well in all stages of the process, from the 
mere absorption of the spines by the substance of the Crinoid, up to the total 
disappearance of the Productus itself, when the Crinoid stem assumes a swollen 
or distorted appearance. From a consideration of this gradual absorption by 
the Crinoid stem there arise two questions: Did the Productus when once 
attached lose the power to free itself ? or, Did the absorption by the Crinoid, 
contrary to the view indicated previously, commence only after the death of 
the Productus?” 
Some of Mr. Etheridge’s figures of this species, which is from the Lower 
Carboniferous limestone of Edinburghshire, Scotland, are here reproduced. 
