

Knowledge of the Spongida. ' 345 



cellous, more or less radiated structure internally well diffe- 

 rentiated " (< Annals/ 1875, vol. xvi. p. 133), now only 

 consists of three groups, viz. Geodina, Stellettina, and Tethyina; 

 but as it seems to me desirable that a fourth should be inserted 

 between the two latter, this will appear hereafter under the 

 proposed name of " Theneanina," for reasons which will then 

 become evident. 



1. Geodina. 



The spiculation of this group, whose characters are detailed 

 at length in my Classification (op. et he. cit. p. 183), con- 

 sists of a " body-" (PI. XIV. fig. l,a), a "zone-" (fig. l,b) 7 

 and " anchoring-spicules " (fig. 1, c), together with a great 

 number of minute globular siliceous bodies, and still smaller 

 stellates &c. or u tlesh-spicules," which are chiefly congre- 

 gated into a hard crust around the exterior; but as some of 

 these elements may be variously formed, it becomes necessary, 

 for memory's sake, to subdivide the group accordingly ; and for 

 this purpose we, of course, select that element which offers 

 the most striking diversity, viz the " zone-spicule." In this 

 we find the following differences : 



Section 1. 



Arms simple and straight (or Orthactiuida). 



a. Radiating more or less forwards. (Proradiata.) 



b. Kadiating horizontally. (Planiradiata.) 



c. Curved outwards or backwards respectively. (Re- 



cur vii'adiata .) 



Section 2. 



and bifur 



a. Radiating more or less forwards. (Proradiata.) 



b. Radiating horizontally. (Planiradiata.) 



c. Curved outwards or backwards respectively, (It 



) 



ill 



i Annals/ 1869, vol. iv. p. 9, pi. ii. figs. 16 a, b) y would 

 thus belong to Section 1, b, the body-spicule here presents 

 the greatest difference, being more or less cylindrical and 

 I obtuse or inflated at both ends (ib. ib. fig. 17) instead of 



fusiform and sharp-pointed, which is the usual form ; while 

 the zone-spicule is so abnormally developed in general that 

 it is the exception rather than the rule to find a perfect one. 

 In Schmidt's genus Caminus (Spong. Adriat. Meeres, p. 48, 



Ann. & Mag. N. Hist. Sen 5. Vol. xi. 24 





