Among the internal septa and the corresponding external constrictions which effect the lobulation of the cephalis, may be distinguished primary or constant septa and secondary or inconstant septa. As primary septa we regard firstly an oblique frontal septum and secondly a vertical sagittal septum. The frontal septum (described accurately by Bütschli) 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 important:—(1) 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 (not here described) in which I could not determine the topographical regions of the cephalis. The difficulty in the examination of these complicated forms is increased by their very small size, which does not reach the usual dimensions of the other Cyrtellaria. In some cases I was able to observe on the base of the cephalis the same typical cortinar pores (in two or three pairs), which we also find in the same part of the cephalis in the Spyroidea and Cyrtoidea, and which are inherited from the Semantida.

The thorax of the Botryodea, or the second shell-joint, absent in the Cannobotryida, is usually of very simple form, ovate, truncate, conical or cylindrical, and consists of a secondary joint, developed from the base of the cephalis. The thorax is usually small, about the same size as the cephalis or a little larger, whilst in the Cyrtoidea it is commonly much larger than the latter. Its terminal mouth is closed by a lattice-plate in the Botryocellida, while it remains open in the Botryopylida and Pylobotryida.

The abdomen, or the third shell-joint, developed in the Pylobotryida only, generally also exhibits a very simple shape, like the thorax, and it is a tertiary joint developed from the base of the thorax. It exhibits to the latter the same relation as in the Tricyrtida. The terminal mouth of the abdomen remains open in the Botryocyrtida; it becomes closed by a lattice-plate in the Botryocampida.

The lattice-plate forming the shell of the Botryodea is usually very thin and fragile, with very small circular pores. These are often very numerous, at other times scarce, and sometimes nearly wanting, so that the shell appears hyaline. In this group there never occurs that great variety in form and size of the pores, which numerous Cyrtoidea and Spyroidea exhibit.

The radial apophyses which are found in the majority of Botryodea seem to correspond in position and relation to the typical radial beams of the other Nassellaria, viz., three descending basal feet arising from the base of the cephalis, and an ascending vertical apical horn arising from the top of the cephalis. Here also they seem to be inherited from the Plectoidea or Stephoidea (Cortina, Cortiniscus). But whilst these four typical radial beams in the other Nassellaria are usually simple spines or solid rods, here they usually appear as hollow cylindrical tubes, the thin wall of which is pierced by the same small pores as the shell. These porous tubes are either straight or slightly curved, often inflated and ovate at the base. We find in their number and disposition the same variety as in the simple radial spines of the other Nassellaria. The original number may here also be seen in the development of four typical beams, an ascending apical tube on the top of the cephalis, and three descending basal tubes on its base; the odd posterior tube of the latter corresponds to the caudal foot, the two paired anterior to the pectoral feet. There is often also a fourth foot developed opposite to the caudal, and representing a sternal tube. Sometimes also two superior tubes are developed, a posterior occipital and an anterior frontal. The different apophyses may be lost by reduction. I have never observed Botryodea with more than five apophyses.

The Central Capsule of the Botryodea is not yet sufficiently known, no living species having been observed. In some preparations from specimens in the Challenger collections, stained by Dr. John Murray with carmine immediately after the dredging operation, single Botryodea are to be found in which the central capsule is deeply coloured. In Botryopera quinqueloba (Pl. [96], fig. 2) it filled up the greater part of the cephalis and seemed to be divided into some small lobes. In Lithobotrys sphærothorax (Pl. [96], fig. 15) it was divided into four lobes, three of which filled the trilobed cephalis, the fourth large lobe occupying a great part of the spherical thorax. Details of their structure, unfortunately, were not recognisable. There can, however, be no doubt that they are the same as in all other Nassellaria.

Synopsis of the Families of Botryodea.
1. Shell monothalamous, consisting of the lobate cephalis only,1. Cannobotryida.
2. Shell dithalamous, composed of a lobate cephalis and a simple thorax,2. Lithobotryida.
3. Shell trithalamous, composed of a lobate cephalis, a thorax and an abdomen,3. Pylobotryida.