ARTICULATA. 4 1 



of calcareous spar, by which the smallest ossicle of star-fish or 

 Crinoid may be recognised : this peculiarity is most strikingly 

 obvious in the great spines of the Cidaris (fig. 8, 3), or the 

 enlarged column of the "pear Encrinite" (fig. 6, 7). Examples 

 of the latter may be seen which had been crushed when 

 recent, and before the sparry structure was superinduced. 



Order 6. — Holothurioidea. 



(Sea- Cucumbers, Trepang.) 



Char. — Body vermiform ; integument flexible, with scattered 

 reticulate calcareous corpuscles, or beset with small 

 anchor-shaped spicula. 



The Holothurioid order presents scarcely any examples 

 likely to be met with in a fossil state, except the genus Psoitis, 

 of whose imbricated shield a fragment has been found by Mr. 

 Eichmond in the northern drift of Bute. Count Miinster has 

 figured the microscopic plates, apparently of a Holothuria, 

 from the chalk of Warminster; and the anchor of a Synapta 

 from a still older formation, — the upper oolite of Bavaria* 

 Microscopic observers will doubtless meet with many such 

 detached plates and spines when searching for Polycystinea? 

 and other Bhizopods in the oolitic and cretaceous strata ; but 

 it is scarcely probable that the order has dated far back in 

 time. 



Province II.— ABTICULATA. 



In the great division of invertebrate animals called Arti- 

 cidata, the brain is in the form of a ring encircling the gullet. 

 A double ganglion above the tube supplies the chief organs of 

 sense. From the ganglion below the tube two chords extend 

 along the ventral surface of the abdomen which are in most 

 species united at certain distances by double ganglions ; with 



* Beitrage, heft 6, 1843. 



