THE STEM AM) CALYX. 88 



one being - hidden beneath the radials. The exposed part, which consists of barelj 

 more than what might he called the lips of the mouth, is slightly projecting along 

 the margin ; it is in form rhomboidal, but the angle toward the radials ie covered 

 by the tips of the overlapping limbs. The concealed portions arc Longer than wide, 



and their distal end is somewhat extended outward and downward." M r. Wachsmuth 

 admits that " the description of the interradial plates was made from a specimen in 

 which the greater part of the limbs had weathered away, thereby exposing the parts 

 underneath;" and we cannot help thinking that he has been misled in consequence, 

 partly, if he will forgive us for saying so, by his having forgotten the structure of 

 the summit of Codaster. He has been kind enough to send us for examination no 

 less than five specimens of Heteroschisma gradle, and has also informed us that the 

 specimen belonging to him, which we figure on PI. X. figs. 19, 20, as Codaster alter- 

 natus, Lyon, is his Heteroschisma alternatum, var. elongatum. We have therefore 

 had six authentic examples of the genus for examination, and after studying them 

 carefully we have come to the conclusion that it cannot he separated from Codaster. 

 For in each specimen, though not in every sinus, we have found the sutures between 

 radials and interradials in exactly the same position as they occupy in Cryptoschisma 

 (PL V. fig. 24; PL XIII. fig. 20), Phcenoschisma (PL XL figs. 1-0), and Codaster 

 (PL XII. figs. 1-0 ; PL XIII. figs. 1, 4, 8). It starts from the distal end of the oral 

 crest where the latter meets the interradial suture, and it descends the sloping sides 

 of the radial sinus cutting the hydrospires and ambulacra nearly at right angles, just 

 as in Codaster Hindei and C. pyramidatus (PL XII. figs. 1-0 ; PL XVI. fig. 1). We 

 do not wonder that these sutures have escaped Mr. Wachsmuth's notice, as they are 

 not easy to see, and are only visible at all upon some of the sinuses. But after our 

 experience with a large collection of the British species, we have no doubt as to the 

 existence of the sutures, both in C. Hindei and in C. pyramidatus, and also in 

 Mr. Wachsmuth's specimens of Ileteroschismec. Owing to the circumstances of their 

 position they are altogether different in appearance from the interbasal or interradial 

 sutures, and manifest themselves by a kind of continuous break in the line of 

 hydrospires, which is difficult to describe, but when once seen in Codaster trilobatus 

 (PL XIII. figs. 1, 4, 8) is easily recognized in other species. 



Thus, then, we believe that the principal character on which Heteroschisma was 

 established has no existence in fact. Let us now pass on to those of a secondary 

 nature. 



Mr. Wachsmuth 1 says that " in Codaster the hydrospires enter the body nearly at 

 right angles, and the walls are placed almost parallel to each other. In Il> 1* roschisma 

 the hydrospires stand obliquely to the sides of the sinus, and they are arranged 

 closely round the mouth, while those of Codeistcr are placed away from the mouth." 

 We are a little doubtful as to the meaning of the first sentence ; but we cannot 

 1 Proc. Davenport Acad. Nat. Sci. 1SS5, vol. iv. p. s :;. 



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