K0ACTTNIDJ3. 



189 



emphasis on the fusion of a radial element with its interradial neighbour. The 

 two together he names a " machoire." The right-hand portion of Scheme D of 

 Viguier, reproduced here as Text-fig. 130, gives a side view of the " machoire." 

 The shading which I have added to the original figure makes the double origin of 



-BMP 



Text-fig. 130. — Scheme D of Viguier. Lettering as in Text-fig.' 131. The " r»acAuircs " are seen both in front 



(adoral) and side view. 



the structure more distinct. The lower unshaded portion is the mouth-angle 

 plate; the upper shaded portion is the first ambulacral. Usually the division 

 between these two ossicles cannot be distinguished without maceration in potash, 



Atti.i. 



V. I. muse- 



R.M; 



Pr.M.R 



TIT. 



B.M.R 



Text-fig. 131. — Adoral view of an angle of the mouth-frame of Culcita. Am. 1, first ambulacral ; Ap., apo- 

 physis ; B.M.P., base of mouth-angle plate; In.M., interradial muscle; n.r., groove for nerve-ring; 

 Pr.M.P., ascending branch of mouth-angle plate ; R.M., radial muscle (muscle abductor des dents) ; 

 J'.T.musc, ventral transverse muscle of first ambulacral ; w.v.r., groove for water- vascular ring, x 3^. 



although occasionally the shrinkage in a dried specimen may make this unnecessary. 

 Viguier's diagram is based on a study of Pentaceros. In order to show the details 

 more clearly I am adding a wash drawing, similarly oriented, of Culcita. 



Viguier, for descriptive purposes, recognised two regions of the mouth-angle 



