SVSTKMATIC ( LASSIKICATIO.V OF |.;< ||| N | 



procumbent (text-figs. 214-216, p. 184) though inclined in Kchinocyamu^ ' Uven, 1892). The 

 teeth are keeled, foramen magnum shallow, cpiphyses small and narrow, h.-.- -mail, wanting 

 in Laganum (Loven, 1892), compasses wanting. The pyramids an- more or le*s highly modi- 

 fied (least in Echinocyamus, Love"n, 1892) with wing-like lateral expan-io,,- and without , 

 for the attachment of interpyramidal muscles. The perignathic girdle con.-i-t- ,,f auridi- only, 

 which are situated on the ambulacral plates (text-fig. 231, p. 197) a.- in tin- (Vntrcchinoida. 

 or may be transferred to the primordial interambulacnil plat.- t.At-di;. -j:<r,. ,,. pi7 . :is -how-M 

 by Loven (1892). Each pair of auricles bears one or two pairs of retract. .r mu-.-l.-s, um | m 

 addition one pair of protractors. This last is a peculiar feature of the group, as in all 

 other Echini with lanterns the protractors are inserted on the interambulacral plate-, or on 

 apophyses arising from the same, but not on auricles. Respiration is apparently by ambu- 

 lacra! gills only. Sphaeridia are situated in enclosed pits (Love"n, 1874). 



The suborder Spatangina is characterized by tests which are conical, heart-haped. or of 

 various forms, often extraordinary (Pourtalesia), but bilaterally symmetrical through III. :, 

 The ambulacral plates are simple and the areas are usually petaloid dorsally. There may lie 

 two pores or one to a plate, or plates may be in part imperforate. The plates may lie low. ..r 

 high, and of very specialized form, especially in the bivium vcntrally. Plate-, i -peeiallv in 

 ambulacrum III, may be high, nearly or quite hexagonal in form, with pore- -upcrpos<-d in 

 the middle of the plate (text-fig. 8, p. 54), a feature not seen in the adults of other form- -incr 

 the Ordovician Bothriocidaris, though common in the young of regular Echini. The primordial 

 ambulacral and interambulacral plates are typically in the basicoronal row 1 Plate 3. (j^. j .-, 

 but, in the shifting of parts, one or the other may in part be pushed dorsally. The l.a-r ..f the 

 corona is apparently never resorbed by the advance of the peristome, which latter i> u-ually 

 densely covered with small non-ambulacral plates (text-figs. 27- 2S, p. 70. and .VI. p. Mh. Ocular 

 plates may be all exsert, that is, do not reach the center line, or ocular> I. V, or I. V. IV. or 

 I, V, IV, II may be insert (text-figs. 172-175, p. 149). In certain specialized l\ 

 in some species of Pourtalesia (LovSn, 1883; A. Agassiz, 1904), the oculars an- apparently 

 partially or wholly absent in adults. Four genitals are typically present, but 5 is absent and 

 more genitals may be wanting. Genitals 2, 3 may be typically fused (( 'yst echinus. A 

 1904), as seen in variants of regular Echini (p. 167). The madreporic pores are in genital 2 

 or extend to 3 where these two plates are fused. An extension to :* i- a common variant in 

 some regular Echini (p. 172). Genital 2 may be much enlarged and extended posteriorly 

 so as to reach interambulacrum 5 (text-fig. 173, p. 149). The lantern is wanting in adults, but 

 occurs in young Echinoneus (pp. 189, 217), as shown recently by Mr. Agassiz ll'.MH)). - 

 are short and undifferentiated, or may be highly produced and with marked arenl differentia- 

 tion. Tubercles in some genera are subject to much areal differentiation, making pattern- 

 on the test. The primary tubercles in Metalia, Meoma, and Brissus are [xrforate and cronu- 



