Tin; iiyi>i;oximi;i:s and 8PIEACLB8. 77 



the tubes and the marginal pores of the ambulacra escaped Ids notice ; though he 

 pointed out that the tubes seemed to obstruct the communication of these pores 

 with the internal cavity of the calyx, a communication which he believed to exist on 

 theoretical grounds as he supposed the pores to represent the nutritive canals of the 

 so-called pinnules. 



Roemer also described the ridges and furrows (or hydrospire-slits) on the ventral 

 surface of Codaster (PI. XIII.), and he rightly compared them to the slits which 

 appear at the sides of the ambulacra in Phcenoschisma caryophyllatum 1 (=Pen- 

 tremites Orfyignyanus, Roemer (non do Koninck) (l'l. XIV. tigs. 1-4)). But as he 

 made no sections of the calyx in either of these two types, the identity of their 

 hydrospire-slits with the tubular apparatus concealed beneath the ambulacra of a 

 true Pentremites altogether escaped his notice. New species of Codaster were 

 described a few years later by both Lyon and Shumard ; but they added nothing to our 

 knowledge of the morphology of the hydrospires. McCoy 2 , however, had recognized 

 in 1849 the resemblance of the hydrospire-slits of Codaster to the pectinated rhombs 

 of the Cystids, and the same remark was made by Hall 3 in 1SG1. 



In the course of the following year two suggestions of very different character 

 were made as to the nature of the hydrospires and of their external openings, the 

 so-called "spiracles." It appeared to White 4 that the prevailing view of the 

 summit-openings as ovarian apertures was not consistent with our knowledge of the 

 mode of deposit and dispersion of the ova of the closely allied Crinoids. He thought 

 it probable that they were the " apertures of siphonal tubes for the vibration of the 

 tentacula, by the injection and expulsion of water ; communicating by way of the 

 tubular apparatus beneath each ambulacral field with each tentacle through the 

 pores, expanding them by the inflation of the tubular canal along their inner grooves, 

 and contracting them by the expulsion of the water. It is conceived that this 

 operation of the siphonal tubes would produce all the necessary motion of the 

 tentacula, and be more in accordance with the status of the animal than a complex 

 muscular system which would otherwise be necessary to operate the hundreds of 

 these minute organs." 



Ingenious as this theory is, it is totally inconsistent with our knowledge of 

 the recent Crinoids. It requires a strong effort of the imagination to conceive that 



1 The hydrospire-slits are incorrectly represented in Roemer's figure of this species. They arc shown as 

 having their proximal ends exposed, and their distal ends concealed beneath the ambulacra ; whereas in 

 reality the reverse is the case, as shown in tho side view of the calyx which is given by Itoemer and in our 

 own figures, PI. XIY. figs. 3, 4. 



2 Ann. & Mag. Nat. Hist. 1849, vol. iii. p. 251. 



3 " Descriptions of new species of Crinoidea from the Carboniferous lioeks of the Mississippi Valley," 

 Journ. Bost. Soc. Nat. Hist. 1861, vol. vii. no. 2, p. 32". 



* Rid. 18G3, vol. vii. no. 4, p. 485. 



