306 THE VOYAGE OF H.M.S. CHALLENGER. 



Family XII. DRUPPULIDA, Haeckel, 1882 (Pis. 15, 16, 17, 39). 



Definition. Prunoidea with ellipsoidal, latticed (not spongy) shell, composed 

 of two or more concentric shells ; a simple or double cortical shell enclosing one 

 or two internal concentric shells (medullary shells), without equatorial stricture. 

 Central capsule ellipsoidal or cylindrical, without annular equatorial constriction. 



The family Druppulida differs from the Ellipsida only in the possession of a 

 simple or double medullary shell, which is enclosed in the centre of the central capsule, and 

 connected with the ellipsoidal cortical shell (lying outside it) by radial beams, perforating 

 the membrane of the capsule. The Druppulida exhibit therefore the same relation to the 

 Ellipsida that the Dyosphserida among the Sphseroidea bear to the Monosphserida. 

 The cortical shell may be simple or multiple. The whole fenestrated shell is thus 

 composed of a variable number (two at least) of concentric shells, which are connected 

 by radial beams. 



The Medullary Shell enclosed in the centre of the central capsule is either simple 

 or double, and composed of two small concentric shells. Their form is either spherical, 

 or ellipsoidal, or lenticular. If the medullary shell be ellipsoidal, the main axis of the 

 ellipsoid is the same^ as in the cortical shell. Sometimes the inner medullary shell is 

 spherical, the outer ellipsoidal or lenticular. If the medullary shell be lenticular (arising 

 from both poles of the main axis) its vertical axis is also identical with that of the 

 cortical shell (PI. 39, fig. 5). 



The Radial Beams, which connect the medullary and cortical shell, are either 

 developed in all possible directions (Pis. 16, 17), or limited to the equatorial plane, more 

 rarely to the meridional plane. Sometimes the connection is produced only by two 

 opposite beams which lie in the minor or equatorial axis (PI. 39, figs. 3, 7, 8) ; more 

 rarely in the major or meridional axis (PL 17, figs. 7, 8). 



The Cortical Shell is constantly ellipsoidal, rarely with modifications, similar to 

 those which appear in the simple shell of some Ellipsida. As a rule it is simple, 

 rarely composed of two or more (sometimes six or more) concentric ellipsoidal shells (in 

 Cromyodruppa and Cromyocarpus). The outer surface is commonly smooth, more 

 rarely covered with radial spines (in Druppoca/rpus, Prunocarpus, &c.). In the 

 majority peculiar polar appendages are developed at both poles of the main axis, these 

 being prolongations of them, either in the form of hollow fenestrated tubes (Pipctta, 

 Pipettaria, PL 39, figs. 7, 8), or solid strong spines. The two p*olar spines are either 

 equal in size and similar in form (as in Lithatractus, Stylatractus) or unequal (as in 

 Dntppatmctus, Xiphatractus, Pis. 16, 17). 



The most primitive of all Druppulida is Druppida, with simple medullary shell and 

 simple cortical shell (PL 39, fig. 3) ; Prunulum differs from it only in the possession 



