76 CATALOGUE OF THE BLASTOIDEA. 



CHAPTER V. 



THE HYDROSPIRES AND SPIRACLES. 



A. Historical. 



The name " Hydrospires " was given by Billings 1 in 1869 to the remarkable system 

 of lamellar tubes which lie between, and more or less beneath, the ambulacra of 

 a Blastoid. In the Codasteridse they open externally on the ventral aspect of the 

 calyx by a series of elongated slits in the interradial areas which lie nearly parallel 

 to the ambulacra (PI. XIII., XIV.) ; while in the Pentremitidce they are entirely 

 concealed beneath the ambulacra, and are only exposed after removal of the lancet- 

 plate and side plates (PI. I. figs. 6, 7 ; PL XII. fig. 13). 



The first author who seems to have taken any special notice of the hydrospire- 

 slits was Troost 2 , who gives a figure of a " Pentremites, the ambulacrum being 

 removed, showing the ridges and furrows," while he speaks of the " interior " of the 

 ambulacrum as being " longitudinally furrowed, forming a number of channels which 

 fit in similar channels of the interior of the body." 



The next reference to these organs with which we are acquainted occurs in 

 the description of Codaster by Professor McCoy 3 , who noticed that four of the 

 interradial areas of the summit " are marked with coarse, rough, parallel stria? 

 nearly coinciding in direction with the pseudambulacral ridges, and converging to 

 the second set of ridges ; the impressed lines between these strke seem punctured, the 

 fifth C? posterior) space is without sulcation." He was unable, however, to make any 

 suggestion as to the nature of this sulcation. A few years later Roemer 4 described 

 for the first time the lamellar tubes which lie beneath the ambulacra of Pentremites, 

 nnd their communication with the exterior through the summit-openings, to which 

 the name " spiracles " was afterwards given by Billings. But the relation between 



1 American Journ. Sci. 1809, vol. xlviii. p. 75 : Ann. & Mag. Nat. Hist. 1869, vol. v. p. 258. 



a On the Pentremites Reinwardtii, a new fossil; with remarks on the genus Pentremites (Say), and its 

 geognostic position in the States of Tennessee, Alabama, and Kentucky," Trans. Gcol. Soc. Penn. 1835, vol. i. 

 p. 227, pi. x. fig. 7. 



3 Ann. & Mag. Nat. Hist. 1849, vol. iii. p. 250. 



< Archiv f. Naturgesch. 1851, Jahrg. xvii. Bd. i. pp. 339-341. 



