PBRIGKATHIC GTEDLE OP THE ECHINOIBEA. 181 



lacral auricles are closely connected, and appear to be more 

 intimately connected than in Glyphostomata, wliere the inter- 

 ambulacral processes on each side of the intervening ambulacral 

 space form an arch which may or may not be closed, and of 

 which the extremity is more or less closely soldered together." 



A. Agassiz gires excellent figures of the auricles and pays 

 much attention to their condition in the Clypeastroids. 



It is perfectly clear that there is a great diversity of opinion 

 between Loven and Agassiz. 



T. H. Stewart gave a description of the jaws and of their 

 muscles and their attachments to the body of the test, The 

 description was accompanied by a drawing, and, as might be 

 expected, they are models of clearness and correctness. 



The form which Stewart investigated (Proc. Zool. Soc. 1861, 

 p. 53) was not one of the Cidaridse, and the origin of muscles 

 from " auricles " and intermediate interradial ridges clearly 

 proves that the arrangement is not the same in the Cidaridse 

 (see J. Mliller's figure) and in the other regular Echinoidea 

 with jaws. 



Charles Stewart examined the structures of Dorocidaris papil- 

 lata and gave an excellent description of the internal branchiae, 

 of the jaw-chamber, and of the compasses and their use. In 

 illustrating his paper (" On certain Organs of the Cidaridse," 

 Trans. Linn. Soc. vol. i., Second Series, Zool, pt. xxii. p. 569, 

 pi. Ixx., 1877) the author gave an excellent figure of the top of 

 the jaws, the compasses and their ligaments, the branchiae, and 

 the part of the test between the ambulacra to which some muscles 

 are attached. 



There are also two admirable drawings of the ambulacra, and 

 Miiller's vertebral processes are well shown ; and their spinulose 

 analogues, which Mr. Stewart noticed curving over the a^mbulacral 

 vessels, are represented *. 



Terminology. — The term " Auricle," taken from fancied resem- 

 blance to little ears of the arched processes of the structures 

 which give attachment to the jaw-muscles, is one which should 

 lapse. 



* Wyyille Thomson held that the structures I call the " perignathic girdle " 

 were distinct from the test. In his essay in the Phil. Trans, vol. 164. pt. ii. 

 p. 731, he states that in the Echinothuridse "the ring of calcareous elements 

 forming the auriculse and their uniting ridges appears to be entirely distinct, 

 merely forming adhesions with the ambulacral and interradial elements." 



