CYSTOIDEA. 449 



question is the mouth. A second aperture (fig. 319, an) is placed 

 excentrically, usually on the upper surface of the calyx, and in good 

 specimens is furnished with five or six triangular calcareous plates, 

 which are arranged to form a sort of cone or " valvular pyramid," 

 and which serve for the closure of the opening. It is not neces- 

 sary to discuss the various views which have been put forward as 

 to the functions of this orifice, but there is every reason to believe 

 that it is really the anus. In many cases there is a third opening, 

 which is always of small size and always placed near the mouth 

 (fig. 319, 0). This aperture has been commonly regarded as being 

 of the nature of an " ovarian " aperture or genital pore. 



In well-preserved examples, the upper surface of the calyx com- 

 monly exhibits simple or branched grooves (fig. 319, am\ which 

 radiate from the mouth, and obviously are of the nature of " ambu- 

 lacral grooves" or "food-grooves." In some cases, as, for example, 

 in Callocystites (fig. 320) and in Lepadocrinus 

 (fig. 326, c), the ambulacral groove is bordered 

 on each side with a row of delicate jointed 

 pinnulse, which are also grooved on their ventral 

 faces. In such cases, the ambulacral grooves 

 may be looked upon as representing recumbent 

 arms which have become soldered down to the 

 surface of the calyx. In cases where the am- 

 bulacral groove is bordered by a single row of 

 pinnules, the arm may be supposed to be fast- 

 ened down to the calyx by one of its sides J^rS^- 

 instead of by the dorsal surface. In other Jewettu, from the Siiu- 



. J nan of North America, 



Cystideans the upper surface 01 the calyx ex- showing the ambulacral 

 hibits irregularly scattered articular facets, which, |[°° v £f JjJ. a p^ n Ses°on 

 in the perfect condition, served for the attach- ^ e sid ^ s °f these •• /> 



r ' Pore - rhombs. (After 



ment of small unbranched jointed filaments. Hail.) 

 These may be regarded as of the nature of 

 "armlets" or simple arms, rather than as pinnulse. They are 

 seen in such genera as Glyptosphcerites (fig. 319, p), Caryocrinus 

 (fig. 326, a), and Pleurocystites (fig. 326, b), and they can be some- 

 times shown to possess a ventral groove, which is provided with 

 small calcareous covering-plates. Lastly, in the genus Comarocystites 

 there are four free arms, which differ from the structures just spoken 

 of, and agree with the arms of the Crinoids generally, in being pro- 

 vided with lateral pinnse. 



In some forms of the Cystideans (Cryptocrinus, Malocystites, &c.) 

 the plates of the calyx appear to be completely imperforate. In the 

 majority of cases, however, the walls of the calyx are more or less 

 extensively perforated by pores or fissures, which usually open 

 directly on the outer surface of the body, but are in other cases 



vol. 1. 2 F 



