1538 THE VOYAGE OF H.M.S. CHALLENGER. 



modified form), without a shell-mouth or a peculiar constant large opening on the 

 lattice-shell ; (B) Phseogromia, with an ovate or polyhedral, not bivalved shell 

 (often also of a subspherical, ellipsoidal, or another modified form), constantly provided 

 with a shell-mouth or a peculiar large opening on one pole of the main axis of the 

 lattice-shell ; (C) Phseoconchia, with a bivalved shell, composed of two completely 

 separated, hemispherical, cap-shaped or boat-shaped valves (a dorsal and a ventral), 

 comparable to that of the Brachiopoda. 



The Phseosphaeria, or those PH^EODAKIA the big shell of which is usually spherical, 

 never bivalved and never provided with a peculiar shell-mouth, comprise a great number 

 of common and large-sized PHJSODARIA, which may be arranged into four different 

 families, according to the different structure of the shell (l) Orosphserida (PL 106, 107), 

 spherical shell extremely big and robust, composed of a single piece of coarse lattice- 

 work, the thick bars of which are stratified and contain partly a fine axial-canal, meshes 

 of the network usually irregularly polygonal, no astral septa in the nodal points ; (2) 

 Sagosphserida (PI. 108), spherical shell large-sized, but extremely delicate and fragile, 

 composed of a single piece of arachnoidal lattice-work, the thin bars of which are simple 

 solid threads, without axial -canal, meshes of the network always large and triangular, 

 no astral septa in the nodal points ; (3) Aulosphserida (PI. 109-111), spherical shell 

 large-sized, but very fragile, composed of numerous hollow cylindrical tubes, which are 

 connected (and at the same time separated) by peculiar astral septa in the nodal points, 

 meshes either triangular or polygonal; (4) Cannosphasrida (PI. 112), spherical shell 

 double, composed of two concentric shells which are connected by thin hollow radial 

 tubes, the inner shell simple, solid or fenestrated, with a shell-mouth on the basal 

 pole, the outer shell composed of hollow cylindrical tubes which are connected by astral 

 septa in the nodal points. The structure of this outer shell is the same as in the 

 Aulospheerida, while the basal mouth of the inner shell brings this family in closer 

 relationship to the Phseogromia. 



The Phaeogromia, or those PH^ODAEIA the shell of which is not bivalved, but 

 provided with a peculiar constant mouth on the oral pole of the main axis, are in 

 general similar to the NASSELLAKIA (Monocyrtida), and may be divided into five 

 different families, viz., (l) Challengerida (PI. 99), shell ovate or subspherical, also often 

 triangular or lenticular, distinguished by a peculiar diatomaceous structure, an exceed- 

 ingly fine tracery of regular hexagonal, very delicate network; (2) Medusettida 

 (PI. 118-120), shell ovate, campanulate or cap-shaped, distinguished by a peculiar 

 alveolar structure, with a corona of peculiar hollow, large, articulated feet around the 

 mouth; (3) Castanellida (PI. 113), shell spherical or subspherical, of ordinary simple 

 lattice-work, usually with a corona of simple solid teeth around the mouth ; (4) 

 Circoporida (PI. 114-117), shell spherical or polyhedral, with panelled or dimpled 

 surface, distinguished by a peculiar porcellanous structure (numerous thin needles being 



