DESCRIPTIONS OF THE 8PECEBS. 2G1 



" hydrospires," and further showed that the ambulacra of Codaster were devoid of pores, 

 the so-called pores being really sockets which received the bases of the ambulacra] 



appendages '. McCoy noticed in 184'.) that the anal interradius lacks the "sulcation" 

 which appears over the rest of the summit ; and further researches hy Billings in 

 L870 showed the full complement of hydrospires to be incomplete by two groups, 

 those of the anal interradius. which is occupied solely by the large vent; while the 

 external openings of the hydrospires are independent, and not united to a common 

 hydrospire-tube, as in other genera of the Blastoidca -. 



Remarks. The definition of the genus given by Prof. McCoy may be taken, on the 

 whole, as accurately describing its characters. The radial plates (McCoy's supra* 

 basals), however, not only "reach to the truncated summit," but they are more or 

 less inturned at the edge of the latter towards the apex, so as to form limbs in the 

 usual way, and enclose narrow radial sinuses. But the summit of Codaster does not 

 present the complexity of structure ascribed to it by Prof. McCoy and other writers. 

 Deltoids are present, appearing as diamond-shaped plates on the truncated summits 

 of well-preserved specimens (PI. XIII. figs. 1, 4, 8). Four of these bear along their 

 median line the " thick rapidly tapering ridges " of McCoy, or, as we term them, 

 oral ridges, which are in no way an abnormal structure, but only represent the crests 

 of the deltoids of other genera. 



These deltoid plates were first discovered by Roemer 3 , who detected the radio- 

 deltoid sutures which start from the ends of the oral ridges, and run transversely 

 across the hydrospire-slits till they disappear under the ambulacra (PI. XII. figs. 1, 

 4, 6 ; PI. XIII. figs. 1, 4, 8). Neither Lyon, Shumard, Hall, nor any American 

 palaeontologist has ever noticed them, however, when describing new species of 

 Codaster ; though, as far as our experience goes, there are few individuals which do 

 not show one or more of the sutures, and the presence of deltoids is at once revealed 

 when the summit is ground away a little (PI. XII. fig. 8). 



"We have been quite unable to detect the supplementary basal plates described by 

 Mr. S. S. Lyon in any species examined by us 4 ; and we need hardly say that we 

 cannot accept his statements as to the " pieces " of the summit which lie between the 

 hydrospire-slits being " evidently capable of" compression or depression. 



After a careful examination of Rofe's material, we are glad to be able to add our 

 testimony to the accuracy of his description of the hydrospire-apparatus in Codaster. 

 As previously stated, there are only eight groups of slits (PI. XII. figs. 1, 4 ; PI. XIII. 

 figs. 1, 4) instead of ten as in the closely allied Phmwschisma (PI. XIV. figs. 5, 11) 



1 American Journ. Sci. 1869, vol. xlviii. p. 80. 



2 See Chap. V. pp. 79, 80. 



3 Archiv f. Xaturgesch. 1851, Jahrg. xvii. Bd. i. pp. 383, 384. 

 * See Chap. II. pp. 18-22. 



