OTSr THE PEETGNATHTC GIEDLE OP THE ECnT>"OTDEA. 179 



On the Perignathic Grirdle of the Echiuoidea. By Prof. P. 

 Maetii^ Duncan, M.B. Lond., P.E.S., P.L.s", &c. 



[Read 19th November, 1885.] 



(Plates XXX. & XXXI.) 



Contents. 



I. Introduction and Terminology. 



II. The Perignathic Girdle of the Cidaridse : in Dorocidaris papillata, 

 Goniocidaris geranioides, and Pkyllacanthus imperialis. 



III. The Temnopleuridse : Salmacis hicolor, Temnopleurus toreumaticvs, 

 Microcyphus zigzag, and Amblypneustes ovum. 



IV. The Echinidae : Echinus norvegicus, E. esculentus, and Psammechinus 

 miliaris. 



V. The Echinometradse : Strongylocentrotus lividus, Echinometra lu- 

 cunter, and E. subangularis. Diadematidse : Diadema setosum. 



VI. The Olypeastridae : Clypeaster (Echinanthus) rosaceus, C. humilis, 

 and Laganum depressum as types. Notice of the structures shown in the 

 photographs of A. Agassiz. 



VII. Conclusions. 



I. Inteoduction and Teeminologt. 



The first definite notice of the nature and use of the peri- 

 gnathic girdle with which I am acquainted, was written by that 

 careful anatomist the late Dr. Sharpey, ]?.E,.S., in the ' Cyclo- 

 paedia of Anatomy and Physiology.' In the article " Echino- 

 dermata " (1839, vol. ii. pp. 33 & 36) he gives views of the parts ; 

 but although he describes the muscles of the jaws and their 

 attachments and origins, and explains the nature of the " auricles " 

 to a certain extent, he disposes very briefly of the ridges or 

 plates which are between the auricles in the Echinus he anato- 

 mized. He may be quoted as follows: — "At its lower edge the 

 shell sends inwards a process in form of an arch over each pair 

 of the ambulacral columns." The figure (10 a, p. 33) shows the 

 arches and also the intermediate structure. On page 36 it is 

 stated : — " The muscles and ligaments belonging to the dental 

 apparatus partly pass between its different pieces and partly 

 connect it with the border of the shell. It will be recollected 

 that the border of the shell forms five processes which rise in the 

 form of arches into its cavity round the lower aperture."—" Two 

 muscles come from every arch." — " Other ten muscles arise in 

 pairs from the border of the shell in the interval between the 

 arches." 



It is evident that Sharpey gave the information which was 

 current at that time aud that the " auricles " were well known, 



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