1106 THE VOYAGE OF H.M.S. CHALLENGER. 



(not here described) in whicli 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 C y r t e 1- 

 1 a r i a. 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 S p y r o i d e a and C y r t o i d e a, and which are inherited from the Semantida. 



The thorax of the B o t r y o d e a, 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, alwut 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 tvibes, 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 



