1528 THE VOYAGE OF H.M.S. CHALLENGES. 



operculum, is often rather short, and bears the same relation to it as the nipple 

 does to the human breast (PI. 104, fig. 2). But usually it is more or less prolonged 

 and often about as long as the radius of the capsule, rarely nearly as long as its 

 diameter (PI. 101, fig. 1). Its form is usually a slender cylinder, sometimes somewhat 

 conical and tapering towards the distal end. It is more or less curved or S-shaped in 

 the majority of preparations (PL 115, fig. 3; PI. 127, fig. 6, &c.). Its thin wall is 

 a direct prolongation of the outer membrane of the capsule, therefore it appears as a 

 direct apophysis of the operculum, when this is detached from the latter. The opening 

 at the distal end of the proboscis, through which the endosarc is thrown out, is circular. 

 The parapylse, or the accessory openings of the central capsule, exhibit in all 

 PH^ODARIA the same form and structure, but vary in number and disposition. They 

 are recognised with difficulty in the smaller species, since they are always of small size, 

 and may be easily overlooked. They seem to be completely wanting in the following 

 families : Challengerida (PL 99), Medusettida (Pis. 118-120), Castanellida (PI. 113), 

 and in single genera of other families, as in Phceocolla (PL 101, fig. 1). The 

 majority of PH^EODARIA seem to possess the two lateral parapylas, first described by 

 Hertwig, placed at a variable distance on each side of the aboral pole, to the right and 

 left (PL 101, figs. 2, 6, 10; PL 103, fig. la; PL 104, figs. 1, 2a ; PL 123, 

 figs. 1, 8a, &c.). The horizontal axis, in which the two parapylse lie, is the frontal 

 or lateral axis ; and the plane, which passes through the three openings of these 

 " Tripylea," is the frontal or lateral plane. The number of the parapylse seems to be 

 variable in the two families, Circoporida and Tuscarorida, which also differ from the 

 other PH^ODAEIA in the peculiar (porcellanous) structure of their shell-wall. The 

 number seems to vary even in the single species of one genus ; and the following cases 

 may be found: (A) a single parapyle, placed on the aboral pole of the main axis and 

 directly opposed to the astropyle (on the oral pole), as in Tuscaridium (PL 100, 

 fig. 8); (B) three equidistant parapylse, one of which is placed in the sagittal plane, 

 and the two others one on each side of it, to the right and left, as in Tuscarora 

 (PL 100, figs. 1-6) ; the three parapylse seem to correspond here to the three long 

 feet, or the tubular aboral apophyses of the shell, which are arranged in a similar 

 manner to the three cortinar feet of the NASSELLARIA ; (C) four equidistant parapylse, 

 placed in pairs on the poles of the diagonal axes of a horizontal plane, as in Tuscarusa 

 (PL 100, fig. 7); they seem here to correspond to the four crossed aboral feet; 

 (D) six to eight or more parapylse, probably in the different genera of Circoporida 

 (Pis. 114-117); perhaps each radial tube, which is surrounded on its base by a 

 circle of pores, here corresponds to a separate parapyle. The number of well-preserved 

 central capsules belonging to the two latter families, however, which I could examine 

 was relatively small, and their examination very difficult ; therefore these numbers are 

 not stated with satisfactory certainty and require a further more accurate examination. 



