172 PAI^AMIC DEEP SEA ECHim. 



Argopatagus a. Ag. 

 Argopatagus vitreus A. Ag. 



Argopatagus vitreus A. Ag., Tioc. Am. Acad. 1879, Vol. XIY, p. 209. 

 Argopatagus vitreus A. Ag., "Challenger" Echinoidea, 1881, i>. 160. 



Pis. XXXII, figs. 1-6 ; XXXVIII, fig. 25 ; XXXIX, fig. 18 ; XLI, figs. 32-35. 



Plate 91, figs. 1-3. 



Genicgpatagus A. Ag. 



Genicopatagus affinis a. Ag. 



Gtenicopatagus afEnis A. Ag., Proc. Am. Acad. 1879, Vol. XIV, p. 210. 

 Genicopatagus affinis A. Ag., " Challenger " Echinoidea, 1881, p. 163. 



Pis. XXXI, figs. 12-22; XXXV % figs. 1-4; XXXIX, fig. 20; XLI, figs. 



38-39 ; XLIII, fig. 13 ; XLV, figs. 20-24. 



Plate 91, figs. 4-7. 



The figures of these species given in the Echinoidea of the " Challenger " 

 hardly bring out sufficiently clearly their relationship and the characters 

 allying them with Palaeotropus, Homolampas, and Phryssocystis. Of these 

 genera, Argopatagus and Palaeotropus have simple ambulacral zones with 

 rudimentary phyllodes, as have also Homolampas and Genicopatagus. 

 Homolampas, Phrissocystis, and Genicopatagus (PI. 91, fig. S) have ill-de- 

 fined petaloid ambulacra, merely indicated by the sudden widening of the 

 ambulacral zones above the ambitus. 



Homolampas (PI. 63, figs. 2, 5) has a peripetalous fasciole as well as a 

 subanal fasciole, as have also Argopatagus and Palaeotropus. With the 

 exception of Palaeotropus, in which the labium is flat and the actinostome 

 pentagonal, the other genera mentioned above all have a prominent labium 

 and a more or less elongate actinostome with a re-entering labium ; this 

 attains its maximum in Phrissocystis (PI. 88, fig. 4), in which the projection 

 of the apex of the labium narrows the actinostome to a marked extent. The 

 labium of Palaeotropus (PI. 87, figs. 5, <S\ lo) is quite short ; it is flanked by 

 only one of the actinal posterior ambulacral plates. In Argopatagus (PI. 91, 

 fig. 2) it is flanked by two, and probably also in Phrissocystis (PI. 88, fig. i)\ 

 in Homolampas by two and a half, and in Genicopatagus by no less than 

 four (PI. 91, fig. 4). In Homolampas (PI. 63, figs, x?, J,) and Pal»otropus (PI. 



