ANNULOIDA : ECHINODERMATA. 149 



longer or shorter, jointed, and flexible stalk. The body is dis- 

 tinct, composed of articulated calcareous plates, bursiform, 

 or cup-shaped, and provided with solid arms, which are pri- 

 marily from five to ten in number, are independent of the 

 visceral cavity, and are grooved on their upper surfaces for the 

 ambulacra. (The position of the body being reversed, the 

 upper surface is ventral ; whilst the dorsal surface is inferior, 

 and gives origin to the pedicle.) The tubular processes, 

 however, which are given off from the radiating ambulacra! 

 canals of the Crinoidea, unlike those of the Echinoidea and 

 Asteroidea, are not used in locomotion, but have probably a 

 respiratory function. The mouth is central, and looks upwards, 

 an anal aperture being sometimes present, sometimes absent. 

 The ovaries are situated beneath the skin in the grooves on the 

 ventral surfaces of the arms or pinnules. The arms are furnished 

 with numerous lateral branches or "pinnulae." The embryo 

 is "free and ciliated, and develops within itself a second larval 

 form, which becomes fixed by a peduncle." (Huxley.) 



Of those Crinoidea which are permanently fixed to the sea- 

 bottom by a jointed pedicle, there exist but a few living 

 forms, of which the best known is the Pentacrinus Caput- 

 Medusa. In this type of the Crinoidea largely represented 

 in past geological epochs the body is composed of a series of 

 calcareous plates, united together so as to form a cup, or 

 " calyx," the bottom of which is continued into a " column," or 

 pedicle, composed of a series of calcareous joints or articula- 

 tions, whereby the animal is fixed to some foreign body. The 

 upper part of the calyx is roofed over by a series of calcareous 

 plates, and is perforated by the apertures of the mouth and 

 anus, the latter being sometimes absent. In the recent species 

 the mouth is central, and there is a distinct anus at one side. 

 The margin of the calyx gives origin to the arms, which are 

 grooved on their upper (or ventral) surfaces for the ambulacra. 

 In the living Crinoids the ambulacral grooves are continued 

 along the upper surface of the calyx to the mouth. In the 

 Palaeozoic Crinoids there is only a single opening on the upper 

 surface of the calyx, which is sometimes central and sometimes 

 lateral, and which serves both as a mouth and anus. In many 

 cases this aperture is level with the surface of the calyx, but in 

 many species it is placed at the summit of a long projecting 

 tube, which is termed the "proboscis." The ambulacral 

 grooves in the Palaeozoic Crinoids are found on the ventral 

 surfaces of the arms, as in the living species ; but instead of 

 being continued over the surface of the body to the mouth, 

 they stop short at the bases of the arms, where they gain access 



