AND ITS RELATIONS TO BECENT COMATTJL^E. 203 



centre of the dorsal surface of the piece, pass over its edge and 

 along the sides towards the ventral surface, but end at different 

 levels (PI. XI. figs. 19 a, c). It is very difficult to say whether 

 basals are present or not. There are processes at two of the 

 angles which might be taken for basals (fig. 19 a) ; but these are 

 absent at a third and difficult to make out in the other two. The 

 diameter of the radial pentagou is considerably greater than that 

 of the centrodorsal ; its wide outer surface is very rough and 

 uneven. The general shape of the articular faces resembles that 

 of some specimens of A. scrobiculata (PL X. fig. 18^), but there 

 are one or two peculiar features. The transverse articular ridge 

 present in nearly every Antedon is absent, but in place of it a 

 strong process runs from each side towards the middle line and 

 then stops abruptly (PL XL fig. 19 a). Just above the inner ends 

 of these two processes is a large transversely oblong hole, which 

 I take to be the central canal ; but if so, there is no ligament-pit 

 below it, while both are represented in the later figure of Quen- 

 stedt's specimen. A short bony bar bridges over this large open- 

 ing on the ventral side and unites the two large triangular muscle- 

 plates, the outer edges of which are thick and everted as in 

 A, scrobiculata. This gives a peculiar appearance to the ventral 

 surface (PL XI. fig. 196), the furrows between the apposed muscle- 

 plates converging to a large pentagonal opening, which is evidently 

 more or less artificial ; its angles correspond with the bony bars 

 above the large openings in the articular faces. 



Diameter 6 millims. ; height 5| millims. ; radials 3| millims. 



XIII. — Antedon scrobiculata. (PL X. figs. 14-18.) 

 Goldfuss, Quenstedt, and. de Loriol* have described under the 

 above specific name a number of Antedons from different horizons, 

 which all resemble one another in certain points, but differ very 

 much in others. They all differ from A. costata in the distal faces 

 of the radials being higher than wide, the reverse being the case 

 in A. costata. The Miinster collection of the Woodwardian 

 Museum contains three specimens of this species, two of them 

 authenticated in Miinster' s own handwriting. One character com- ' 

 mon to them and to the other known examples of the species is 

 the shape of the central funnel. This is not a simple pentagon, 



* ' Swiss Orinoids,' p. 255 (with literature). 

 LINN. JOIJBN. — ZOOLOGY, VOL. XV. 16 



