1104 THE VOYAGE OF H.M.S. CHALLENGER. 



I completely separated the Botryodea (or Botrida) from the other suborders of 

 Cyrtellaria (Spyrida and Cyrtida). 



Biitschli gave, in 1882, in his paper on the Cyrtida (loc. cit.)avery accurate descrip- 

 tion of Lithobotrys geminata, and pointed out its close affinity to Lithocorythium and 

 Lithomelissa, and the importance of an oblique septum separating the cephalis into a 

 smaller anterior and a larger posterior lobe. His views on the Botryodea (as a 

 subordinate group of the Cyrtoidea) are however incomplete, since the peculiar 

 forms, described in the following pages, were unknown to him. 



According to the wide morphological divergence of the different Botryodea, and 

 the numerous peculiar forms developed from it, we here divide the whole group into 

 three families and ten genera, with fifty -five species. These form, however, only a small 

 part of the large and varied mass of closely related forms which are found in the rich 

 collections of the Challenger. The great difficulty of researches on their intimate 

 structure, and the great amount of time required for it, prevented me from giving a 

 more complete and exact description than the one here given. The observation of the 

 small shells from all the different sides is a difficult task, requiring years of work, and its 

 satisfactory explanation would be possible only by means of numerous figures. 



The three families of Botryodea, here described, correspond to the three first 

 groups of Cyrtoidea. The first family, Cannobotryida, corresponds to the Mono- 

 cyrtida clausa and to the Zygospyrida ; their shell consists of a cephalis only, without 

 subsequent joints. The second family, Lithobotryida, corresponds to the Dicyrtida and 

 Phormospyrida ; their shell is composed of a cephalis and a thorax, both joints being 

 separated by a transverse cortinar septum and a collar stricture. The third family, 

 Pylobotryida, has a three-jointed shell, like the Tricyrtida, with cephalis, thorax and 

 abdomen. 



The cephalis is the most characteristic part of the shell of the Botryodea and 

 its lobulate and multilocular shape separates them from the Spyroidea and C y r- 

 toidea. It represents the whole shell in the Cannobotryida, and in the young 

 state of the two other families, which afterwards develop a thorax (Lithobotryida) and 

 an abdomen (Pylobotryida). The typical lobulation of the cephalis is probably 

 originally caused by internal septa ; and these may be originated by branches of the 

 internal columella, which corresponds either to the central ascending columella of the 

 Plectoidea or to the excentric ascending dorsal rod of the sagittal ring of the 

 Stephoidea. But afterwards, when the original septa disappear and are lost by 

 reduction, only the external constrictions remain to indicate the limits of the single 

 lobes. 



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 



