REPORT ON THE CRINOIDEA. 165 



I suspect that tliese tunnels lodged not only the food-grooves, but also the nerves, blood- 

 vessels, and water-vessels ; for no recent Crinoid has any calcareous structure between 

 the epithelium of the food-groove and the under surface of the water-vessel. But there 

 is often a tolerably definite plating which extends inwards from the side plates toward the 

 median line of the ambulacrum, beneath the water-vessel (PI. LIV. fig 1 1 ; PI. LVII. 

 fifT. 4, suh ; PI. LXII.) ; and I suspect therefore that the lower row of plates flooring the 

 ambulacral tunnels may be of this nature. Possibly, however, they should be regarded as 

 subambulacral plates better defined in character than those of recent Crinoids, though I 

 am inclined to doubt this, owing to their alternate arrangement. Wachsmuth has dis- 

 covered that the proximal ends of these ambulacral tunnels are connected by a circular 

 vessel which encloses more or less of the upper part of the convoluted digestive organ. 

 The lower part of this structure, with its floor of minute interlocking plates, was obviously 

 the water-vascular ring ; and the five interradial openings in its floor were referred to by 

 myself in 1879^ as indicating the position of the water- tubes which depend from the 

 water-vascular ring into the ccelom, and serve to admit water into the ambulacral system, 

 a view which has been adopted by Zittel. Rhizocrinus lofotensis has only one water- 

 tube in each interradius, which seems also to lie the case in Actinocrinus verneuilianus. 



Besides the ambulacral skeleton, we also find in the Palteocrinoids representatives of 

 the anambulacral plates of Pentacrinus and Comattda. In describing some natural casts 

 of the visceral mass of Actinocrinus, Messrs. Wachsmuth and Springer ^ say " the inter- 

 palmar fields are composed of a soft skin, but although this is more or less encrusted with 

 limestone particles, which sometimes almost look like vault pieces, they have no affinities 

 with the plates of the vault;" while in some specimens of the Actinocrinidae ^ "almost 

 the entire test is lined with a delicate calcareous plexus or network. This lining is not 

 in contact with the test directly, but connected with it by small partitions, producing 

 innumerable little chambers, which communicate with each other and with the visceral 



cavity The structure extends but little below the region of the second radials, 



leaves passages at the arm-openings, and toward the vault " reaches to a place near the 

 median portion of the ray, leaving at the centre an open space in the test which is 

 occupied by the central vault piece." This open space, lying beneath the central one of 

 the apical dome plates and uniting the five ambulacra, was evidently the peristomial area 

 like that of recent Crinoids (PL XVII. fig. 10 ; PL XXVI. figs. 1,2; PL XXXIX. fig. 2 ; 

 PL L. fig. 2 ; PL LV.) ; while the calcareous network within the vault is divided by the 

 ambulacra into five interpalmar fields. It corresponds to the limestone particles on the 

 surface of the internal casts, and represents the anambulacral plates developed in the 

 perisome of recent Crinoids. 



These important observations go to show the complete resemblance between the 



■ Quart. Journ. Micr. Sci., 1879, vol. six., N. S., p. 185. 



2 Revision, part ii. p. 31. ^ Revision, part ii. p. 26. 



