248 PEOF. p. M. DUNCAN'S KBTISIOK OF THE 



Grenus Beissopsis, Agassiz, 1840, Cat. Syst. Ectyp. p. 16 ; 1847, 

 Gat. Bais. d'Ech., Ann. d. Sci. Nat. ser. 3, vol. viii. p. 15, 

 Gray, 1855, Cat. Bee. Ech. Brit.Mus. p. 55. Desor, 1858, 

 Synopsis, p. 378. Loven, 1874, Etudes, pis. xii. & xxxvi. A. 

 Agassiz, 1872-4, Bevision, pp. 354, 593. Dames, 1877, Ba- 

 IcEontographica, Bd. xxv. p. 678. Duncan 8f Sladen, 1884, Bal. 

 Ind. ser. xiv., Boss. EcTi. W. Sind, pt. iii. p. 203. A. Agassiz, 

 1883, ' Blake ' BcJiini, p. 69. (Amended.) 

 Syn. Kleinia, Gray ; Toxohrissus, Desor ; DeaTcia, Pavey ; 

 VerbeeUa, Fritsch, 1877. 



Test thin, moderate in size, ovoid or elongate-oval-elliptical in 

 tumid marginal outline, depressed, lowly tumid dorsally, rounded 

 in front and with a variable, shallow, anterior groove, truncated 

 posteriorly, projecting and convex actinally and behind the peri- 

 stome, or sub globular. 



Apical system central or excentric in front ; four basal plates ; 

 the pores large ; the madreporite in the right anterior basal and 

 passing centrally in the system and posteriorly so as to separate 

 the posterior radial plates and some of the posterior interradial 

 plates also. 



Ambulacra diverse, unequal; the anterior slightly sunken 

 dorsally, with small pairs of close pores most numerous abactinally ; 

 the antero-lateral sunken, subpetaloid, short, equal to but may 

 be longer than the posterior pair, straight, divergent, or curved 

 more or less; pairs of pores large and in parallel rows, with small 

 interporiferous areas. Postero-lateral ambulacra straight or 

 curved, sunken ; pairs of pores as in the antero-lateral, but the 

 anterior row may become continuous with the posterior row of 

 the antero-lateral ambulacra, subpetaloid and tending or not 

 to close at the fasciole ; actinally the areas are bare and large, 

 those of the postero-lateral form wide areas at the sides of the 

 plastron, and four (the 6-9 inclusive) plates of the rows nearest 

 the plastron are angular, with large pores, and are within the 

 subanal fasciole. 



Interradia narrow apically, large actinally ; the right posterior 

 witb normal heteronomy of its plates (union of 2 and 3 of series 

 a). A symmetrical amphisternum. Tubercles small and crowded 

 abactinally, larger actinally, largest at the margins of the bare 

 ambulacra near the peristome. Periproct, in the truncated pos- 

 terior surface, elliptical or ovoid, longitudinal. 



