EEPORT ON THE RADIOLARIA. 1105 



septum and secondly a vertical sagittal septum. The frontal septum (described 

 accurately by Biitschli) has usually two or three pairs of pores and ascends obliquely 

 from the base to the anterior face of the cephalis, where it is inserted in the orbital 

 region ; it divides the cephalis into a smaller anterior or facial lobe and a larger 

 posterior or occipital lobe. The latter is commonly higher and more developed than 

 the former and partly covers its upper face, like the crest of a helmet. The facial lobe 

 is again bisected by an incomplete sagittal septum and a corresponding partial 

 constriction on the anterior face. We find, therefore, in this original cephalis of the 

 Botryodea, three primary lobes, an odd larger occipital lobe and two paired smaller 

 facial lobes. The typical trilobed cephalis may be regarded perhaps as the common 

 original form of the Botryodea. 



The secondary and inconstant constrictions which we find in many Botryodea, 

 and which produce a greater number of lobes in the cephalis, require further accurate 

 observation. The following cases of lobation may be considered as the most im- 

 portant : (l) Cephalis with four lobes, opposite in two pairs (two larger occipital 

 and two smaller facial lobes, separated by a complete sagittal and an oblique frontal 

 constriction) ; (2) cephalis with four unequal lobes, two of which are odd and sagittal, 

 two paired and lateral (the odd occipital lobe usually larger and the odd mandibular 

 lobe smaller than the two paired lateral or buccal lobes) ; (3) cephalis with five lobes 

 (a large odd occipital lobe and two pairs of smaller lobes, anterior nasal, and lateral 

 buccal lobes) ; (4) cephalis with five lobes, three of which are odd (a posterior occipital, 

 middle frontal, and anterior facial lobe), and one pair of lateral lobes ; (5) cephalis with 

 six lobes, opposite in pairs (two larger occipital, two smaller nasal and two intermediate 

 lateral or buccal lobes); (6) cephalis with six lobes, two of which are odd and sagittal 

 (a large occipital and a smaller nasal lobe), four opposite in pairs (two anterior and two 

 posterior buccal lobes) ; (7) cephalis with seven lobes, three of which are odd (a large 

 posterior occipital, a middle frontal, and an anterior small nasal lobe), four opposite in 

 two pairs (an anterior buccal and a posterior temporal pair) ; (8) cephalis with eight 

 lobes, two of which are odd (a large posterior occipital and a small anterior frontal lobe) 

 and six opposite in three lateral pairs ; (9) cephalis with nine lobes, three of which are 

 odd (an occipital, a frontal and a nasal lobe) and six opposite in three lateral pairs ; 

 (10) cephalis with ten lobes, two of which are odd (a large occipital and a smaller 

 frontal lobe) and the other eight opposite in pairs ; (11) cephalis with numerous lobes 

 (twelve to fifteen or more) which are symmetrically disposed on each side of the 

 median plane ; (12) cephalis with numerous lobes (twelve to fifteen or more) which are 

 irregularly and sometimes spirally conglomerated. 



All these different forms of lobation require a far more thorough examination than 

 I can devote to them, and may furnish examples of regular laws of development. The 

 irregular forms are rather common, and I have found some very irregular Botryodea 



(ZOOL. CHALL. EXP. PART XL. 1886.) Rr 139 



