REPORT ON THE RADIOLARIA. 1711 



The family Concharida and the two following closely allied families, the Coelo- 

 dendrida and Ccelographida, compose together the most remarkable and interesting 

 suborder ofPhseoconchia (or " PH^ODARIA bivalva "), differing from all the other 

 Radiolaria in the possession of a bivalved lattice-shell, composed of two separate valves, 

 like the shell of a Brachiopod. The central capsule is so enclosed between the two 

 fenestrated valves that its three openings lie in the horizontal open (frontal) fissure 

 between them, the astropyle or main-opening on the oral pole of the main axis ; the 

 two secondary openings or parapylse on the two sides of its aboral pole, at right and 

 left. The plane in which the three openings lie is therefore the frontal plane, dividing 

 the entire body into a dorsal and a ventral half. The two valves, accordingly, must 

 be considered as dorsal and ventral valves (as in the Brachiopoda), and the symme- 

 trical halves of each valve as right and left. These halves may be always easily 

 distinguished, since the oral pole of each valve is constantly different from the aboral 

 pole. The voluminous phseodium always lies in the oral half, and the central capsule in 

 the aboral half of the shell-cavity, whilst the calymma encloses the whole shell. 



The Concharida differ from the other two families of bivalved PH^EODARIA in the 

 absence of the apical galeas, and the branched hollow tubes arising from them. Each 

 of these two cupolas, which are at the opposite poles of the sagittal axis (one cupola on 

 the apex of each valve), is in the Coelographida connected by a simple or double frenulum 

 with a peculiar rhinocanna, or an open nasal tube directed towards the mouth ; whilst 

 the cupolas of the Ccelodendrida possess neither a rhinocanna nor a frenulum. The three 

 families of Phseoconchia may therefore represent a phylogenetical series, the 

 common root of which are the Concharida. From these are developed the Ccelodendrida 

 by development of an apical cupola or galea on each valve, and of hollow radial tubes 

 arising from it ; whilst the Ccelographida are developed from the latter by production of 

 a rhinocanna on the base of each cupola, and of one or two frenula connecting the 

 former with the latter. 



All the Concharida described in the following pages (seven genera and thirty 

 species), are perfectly new to science, and not a single form of this interesting family 

 was known before the explorations of the Challenger. Some species (mainly of the 

 genera Conchidium and Conchopsis) are by no means rare, and are found in great 

 numbers at some stations of the tropical seas (in the Pacific as well as in the Atlantic). 

 All described species are closely allied, agree in the majority of characters, and are 

 easy to distinguish from all the other Radiolaria. Some few forms of Concharida, 

 however, form a direct passage to the Ccelodendrida. 



Regarding the probable origin of the Concharida (and therefore also of all other 

 Phseoconchia derived from the latter), two different hypotheses are possible. 

 They have either been derived directly from the skeletonless Phceodina, by development 

 of a bivalved lattice-shell ; or they may be derived from PH/EODARIA with a simple 



