THE STEM \\l> «'\i.\ \. 31 



between the intemulials of Codaster ami those of Weteroschisma, as described by 

 Wachsmuth, are so great that, did we believe them to exist, we should be compelled 

 to place Heteroschisma in a separate family by itself, it appears to us, however, 

 that Mr. Wachsmuth's description of Jleteroschisma is an erroneous one — partly, we 

 believe, from his not having clearly understood the real characters of Codaster. He 

 tells us, tor example, that, the interradials of Codaster " rest with their lateral sides 

 against the inflected upper part of the limbs, and form more or less strongly marked 

 edges or elevated angular ridges, which extend out interradially from near the oral 

 opening to the end of the plates. The hydrospires are placed to both sides of the 

 so-called ' oral ridges,' and are located within the limits of the interradials, only 

 small portions of them being continued along the sides of the limbs." lie then goes 

 on to contrast with these statements his description of the interradials of Hetero- 

 schisma. Unfortunately, however, the last sentence in the passage just quoted con- 

 tains an error which affects the whole of Wachsmuth's subsequent account of 

 Heterosclrisma. In the first place, if the hydrospires of Codaster are all located 

 within the limits of the interradials, it is difficult to see how even small portions of 

 them can be continued along the sides of the limbs of the radials. The two state- 

 ments are inconsistent. As a matter of fact, however, the hydrospires of the type 

 species {Codaster trildbatus) are about equally distributed upon the radials and 

 interradials. as is evident from a glance at figs. 1, 4, & 8 on PI. XIII. The faint 

 sutures which separate the diamond-shaped interradials from the limbs of the radials 

 outside them were distinguished by Koenier in the better preserved among his speci- 

 mens, and appear in two of his figures 1 , while they are also shown in the diagram 

 given by Billings -. We cannot but think that Mr. Wachsmuth must have altogether 

 forgotten the position of these sutures wdien he committed himself to the statement 

 that the hydrospires of Codaster are all located within the limits of the interradials. 

 In the British Codaster the summit is nearly flat (PL XIII. figs. 3, 8-12), the ambu- 

 lacra and the oral ridges lying a little above the general plane of the interradial 

 areas. In C. Hindei, and more especially in C. pyramidatus, the summit is excavated 

 in the direction of the ambulacra, which fall away towards their outer ends, so that 

 they lie in shallow sinuses (PL XII. figs. 2, 5). The crest between every two radial 

 sinuses is formed by the oral ridge, and from its outer end, where it meets the limbs 

 of the radials, the sutures slant downwards and inwards so as to meet the ambulacra 

 nearly at right angles, very much as they do in C. trilobatus (PL XII. figs. 1, 4 ; 

 PL XIII. figs. 1, 4, 8). They are, however, difficult to see, and hut for our previous 

 experience with the British species we should probably never have detected them 

 at all. 



Now, according to Wachsmuth the summit of Ueterusehisin>i is rather deeply 



1 Archiv f. Xatuigesch. 1851, Jahrg. xvii. Bd. i. p. 383, Taf. v. figs, 2 A. 2d 



- American Joum. ScL 1869, vol. xlviii. p. 79, fig. 8; Am.. & Mag. Nut. Bist. L870, voL v. p. 1'iil 



