ECHINOIDEA. I. 



H7 



on all the ambulacral plates. The scrobicular areas join on the actinal side as far as to the ambitus. 

 ( hi the abactinal side the primary tubercles decrease very much in size. The secondary tubercles form 

 at the ambitus a tolerably distinct longitudinal series inside of the primary one, but they are con- 

 siderably smaller than the primary tubercles. There are generally a couple of small tubercles just 

 inside of each arc of pores. Besides numerous small tubercles are found on the actinal side, a few- 

 ones on the abactinal side. 



The interambulacral areas (PI. XV. Fig. 17). The primary tubercles form a strong, uninter- 

 rupted longitudinal series, but the scrobicular areas do not touch each other on the actinal side; on 

 this side they are only little larger than the ambulacral primary tubercles, on the abactinal side con- 

 siderably larger. In large specimens they decrease only very little in size towards the apical area, in 

 smaller specimens, on the other hand, they decrease very much in size, so that the whole abactinal 

 side gets a strikingly smooth and naked appearance, the secondary tubercles being here also very few. 

 The actinal side is closely set with secondary tubercles forming a distinct longitudinal series inside of 

 the primary one, and the tubercles of this series may be almost as large as the primary ones. Out- 

 side of the primary series the secondary tubercles are scattered, not placed in longitudinal series. The 

 miliary tubercles are generally few in number and little conspicuous, so that they do not deprive the 

 abactinal side of its smooth character. 



The apical area (PI. XVI. Fig. 8) is most frequently somewhat raised, especially the inner edge. 

 The form of the apical plates show no peculiarities; there is generally a circle of tubercles along the 

 inner edge. In some specimens two pores may be found in one or a couple of the genital plates. 

 The periproct is rather large, covered by numerous small, irregular plates, among which the central 

 plate may be distinct; the plates nearest to the anal opening are a little lengthened, thick, irregularly 

 club-shaped. On specimens in alcohol only these knobs are seen nearest to the anal opening, so that 

 it looks as if the other part of the periproct were naked (Koehler 226. p. 94); in dried specimens the 

 whole area is distinctly seen to be covered with small plates. — In the description by Daniels sen 

 the curious expression occurs: the membranous portion (periprocte) is closely covered with round cal- 

 careous vessels-; this, 110 doubt, is owing to the fact that an erratum in the Danish text, Kalkkar in 

 stead of Kalkkorn , has passed into the English text, which has thus got the meaningless expression 

 calcareous vessels in stead of calcareous grains . 



The buccal membrane contains numerous large, thin, highly perforated calcareous plates 

 (PI. XXI. Fig. 27); those inside of the buccal plates are much smaller and almost without holes 

 (PI. XXI. Fig. 18. a). There is a slight indication of a radiate arrangement of the inmost plates. Very 

 few or no bihamate spicules in the buccal membrane. No spines on the buccal plates; only in larger 

 specimens a few pedicellarias are found outside the buccal plates. The gills with the usual irregular 

 calcareous plates and a few bihamate spicules. 



The length of the spines is very varying, as is seen from the noted measures; thus in two 

 specimens of a diameter of 45 mm the longest spines in one specimen are 22 mm , in the other 43"™. In 

 some specimens the spines are even longer than the diameter of the test, as is especially seen in the 

 statements of Koehler. All the specimens of Koehler seem to have been long-spined; among 

 those from the Ingolf only a few long-spined specimens are found (especially from st. 78), in most 



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