POTERIOCRINID.E EXTRACRINUS. 105 



joint is perforated for the passage of muscles or elastic fibres, there must have been 

 a reo-ular system of muscles which ramified to the remotest extremities, and gave 

 motion to the wonderful frame work, so that the number of muscles in a single 

 adult E.rfracrinus Briareus must have been but little short of one million and a half. 

 The number of joints or ossicula may be apportioned to the several parts as under. — 



Pieces composing the dorso-central plate 5 



1st series of lateral pieces 5 



2nd series of ditto, (jointed) 20 



6 Main rays, of 2 joints each 10 



5 pair of Secondary rays, (arms), each of seven articulations 70 



Twenty leading rays, each consisting of 200 ossicula 4,000 



Three hundred and sixty lateral rays, each consisting of at least 100 joints 3G,000 



Tentacula. — One preceding from each of the forty thousand joints of the main 



secondary and lateral or lesser rays 400,700 



Column. — Number of ossicula, at least 900 



Side Arms. — Taking tlie average number of ossicula in each side arm, at 100 ... 300.000 



Total 741,710 



In this calculation the column has only been considered as being thirty three inches 

 in length, although there can be little doubt that it was frequently more than double 

 that number of inches ; and the side arms are taken as though composed of only 

 one hundred joints each, whereas many of them contain upwards of one hundred and 

 twenty four ossicula. The number of joints in the tentacula are also considerably 

 greater than we have founded our calculation on. Each according to its position has 

 from fifteen to twenty four ossicula. We have only multiplied them by ten. 



It will be seen by our making these deductions that there has been no desire on 

 our part to indulge in exaggeration when dissecting these wonderfully constructed 

 animals, but that we have been more inclined to diminish than to exceed the due limits. 

 At the same time we are convinced that were it possible to count every joint and plate 

 in a full grown Extracrinus Briareus, the total amount would exceed a million. 



We have been diffuse in describing this species, not only on account of the errors 

 which we conceive many palaeontologists have fallen into respecting its structure, but 

 because it is the earliest known crinoid in which the beautiful stellular crenated 

 markings appear on the facets of the columnar joints, a form of structure common to 

 the crinoids of the lias and subsequent formations down to those inhabiting the recent 

 seas. 



