REPORT ON THE RADIOLARIA. 605 



Family XXIV. L arc arid A, Haeckel, 1883 (PL 50, figs. .1, 2). 



Definition. — Larcoidea with a regular, completely latticed, lentelliptical cortical 

 shell, without open gates and annular constrictions ; medullary shell absent or simple 

 (not trizonal), connected with tlie cortical shell by radial beams. 



The family L a r c a r i d a opens the long series of Larcoidea as the most simple 

 group of this suborder. It commences with Cenolarcus, a quite simple lentelliptical 

 latticed shell, which is characterised by three unequal isopolar dimensive axes, perpen- 

 dicular one to another. The major of these three axes is the longitudinal or princijjal, 

 the middle is the lateral or transverse, and the minor is the equatorial or sagittal axis 

 (as in the human body). Among the three dimensive planes, which are determined by 

 pairs of these axes, the lateral plane is the largest (halved by the crossed principal and 

 lateral axes). The intermediate is the sagittal plane or median plane (halved by the 

 crossed principal and sagittal axes). The smallest is the equatorial plane or transverse 

 plane (halved by the crossed lateral and sagittal axes). Therefore the shell has all 

 the characters of the true Lentellijysis or of the " triaxial ellipsoid," and its axes agree 

 with the three axes of the " rhombic crystalline system." 



In the three suljfamilies of Larcarida this lentelliptical shell assumes a different shape : 

 in the Cenolarcida it remains simple, in the Spongolarcida it becomes spongy (sometimes 

 quite filled out with a spongy framework), in the Coccolarcida it is composed of 

 two or more concentric lentelliptical shells (at least an inner medullary and one outer 

 cortical sheU). These shells axe simply connected by radial l^eams, and not, as in the 

 Larnacida, by latticed wings (or half girdles). 



The network of the Larcarida shell is sometimes regular, commonly irregular (as in 

 the greater number of Larcoidea). The surface of the shell is sometimes smooth 

 or thorny, at other times covered with radial spines. These are often symmetrically 

 disposed, either on the poles of the dimensive axes or in crossed diagonal planes. 



The central capsule is a true " lentellipsis " in a geometrical sense ; it is halved by 

 three elliptical dimensive planes of difierent sizes, perpendicular one to another. In 

 the Cenolarcida the central capsule lies freely inside the simple (cortical) shell, only 

 separated from it by the jelly-mantle. In the Coccolarcida it contains the medullar}- 

 shell, and is enclosed by the simple or double cortical shell, perforated l)y the radial 

 beams connecting the two shells. The spongy shell of the Spongolarcida exhibits a 

 different relation to the central capsule : in Spongolarcus the latter lies freely in the 

 internal cavity of the spongy shell ; in StfpoJarcus, where this cavity is quite filled 

 with a spongy network, the central capsule also contains a part of it. 



The morphological and phjdogenetic relations of the Larcarida to the other 

 families of Spumellaria admit of a different explanation. As this famil}' contains the 



