ANATOMY OF OPHIOTHEIX VARIABILIS, ETC. 



119 



would enable great downward bending as well as lateral move J 

 ment to occur; the long umbo and the corresponding socket 

 would allow of a much greater amount of movement than is usual 

 in Ophiothrix for instance, and the nodules on the aboral side 

 would keep the umbo from slipping out. 



DESCRIPTION OF THE PLATES. 

 Plate X. 



Fig. 1. The upper part of the arm, four of the six arm-bones, mouth-frames. 



jaws, and teeth of Ophiothrix variabilis, nob. Magnified and parth 

 diagrammatic, g, genital plate; a, top of arm-bones; mf t mouth- 

 frame ; ;', jaw ; mi, interradialis aboralis muscle of one side of the 

 mouth- frames. 



2. Jaw-plate, magnified, adoral surface. Foramina for the muscles, pro- 



jections for the bases of the tooth -papil lag. 



3. Side view of a longitudinal section made, radially, through teeth, jaw- 



plate, and jaw. j, jaw ; jp, jaw-plate ; c, depressions in the adoral 

 surface of the jaw for the mterradiales adorales muscles, which may 

 be seen passing through the section of the foramina in the jaw -plate to 

 the bases of the teeth, t. Diagrammatic and magnified. 



4. Side and basal view of a large tooth-papilla. Magnified. 



5. Lower surface of the uppermost tooth-papilla;. 



6. Upper view of a tooth and of its base. Magnified. 



7. The two upper foramina of a jaw -plate, showing muscle-slips coming 



out, to be inserted in the base of a tooth, one on each side, magnified. 



8. Adoral view of combined jaws : c, depressions for the muscles. Below 



are the vertical ridges on either side of the central groove. 



9. Under surface of the radial shield, magnified, showing the tuberosity, t, 



the ridge, r, for the retractor, and the remains of the adductor, am. 

 Magnified. 



10. Aboral end of the radial shield and genital plate : r, ridge for retractor : 



f*, ridge for the same onithe genital plate ; g, head of genital plate, in 

 contact above with the tuberosity of the radial shield ; the fibres of 

 the retractor are indicated. Magnified. 



11. Side view of radial shield and genital plate. Same letters as before. 



Magnified. 



12. Side view of the aboral end of the radial shield and genital plate. 



showing the small muscular slip, m, to the genital scale, which is not 

 figured. Magnified. 



13. Upperside of genital plate and shield : gs, genital scale ; ms, muscle- 



slip from genital plate to shield ; am, adductor muscle on its raised 

 attachment. Magnified. 



14. Under view of the genital plate, magnified. 



15. Genital plate, side view towards the genital scale: r*, ridge; p, nodule 



for articulation with the scale. Magnified. 



