KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 



25. 



n:o 



2. 



111 



in the posterior interradius, they abut laterally on one another. The food-grooves pass 

 from the arms över the depressed edges of the deltoids. Thus in a specimen from which 

 the covering plates have been removed, (e. g., h) there is seen a wide semicircular depres- 

 sion or channel. In the middle line of this is a fine, verv distinct groove; and at the 

 bottom of this groove ean be seen with a microseope the suture between the two deltoids, 

 very faint it is true, but distinctly traceable. At the outer end of the inter-deltoid chan- 

 nel is the noteh in the radial through which the axial canal passes almost vertieally 

 downwards, being separated from the food -groove at this point by the deltoid arch. At 

 the inner or adcentral end of the inter-deltoid channels the food-groove passes directly 

 into the peristome; this is pentagonal, with radial angles, and is bounded on four sides 

 by the deltoids, on the fifth side by another plate not previously mentioned — the 

 madreporite. (Plate V, fig. 153). 



The covering plates of the ambulacra pass from the arms along the inter-deltoid 

 channels, and when they are removed the depressions for their attachment to the deltoids 



Text-H»-. 14. Euspirocrinus spiralis, tegmen; 

 speoimen c, X 3 diam. 



Text-fig. 15. Euspirocrinus spiralis, tegmen: 

 specimen d, X 3 diam. 



are verv clearly seen, as in specimens d and //. The food-grooves appear to branch almost 

 before leaving the tegmen, as in some species of Crotalocrinus. This is dne to the lowness 

 of the primibrachs. 



There is however an appearance of branching produced by the presence of certain 

 small plates, which have really no connection with the ambulacra. These are perisomic 

 interambulacral plates, which begin to börder the ambulacra about half-way down the 

 inter-deltoid channel, and which continue to börder tliem for a short distance along the 

 arms, perhaps even as far as the tertiobrachs. In addition to this they give off branches, 

 consisting of a single line of plates, which pass along the suture-lines between the radial 

 and the first braehial, and between succeding brachials, at least as far as the suture be- 

 tween the secundaxil and first tertiobrach. As they pass to the dorsal side of the arms, 

 these plates gradually lessen in size and disappear. When these small plates are removed 

 there are still seen along the suture-lines the indentations made by them, just like the 

 impressions left by the covering-plates. (Compare Streptocrinus, p. 124). 



