REPORT ON THE CRINOIDEA. 187 



remain altogetlier undeveloped. The apical system consists of a dors ocentral plate, 

 basals, and radials, with the frequent addition of under-basals and interradials. These 

 plates form a cup, which either simply supports, or more or less completely encloses the 

 visceral mass, and often bears jointed appendages, the arms and pinnules. 



An oral system, consisting of a central plate (orocentral) and five orals is developed 

 above the peristome of the larva to a very variable extent, and may be either altogether 

 resorbed, or reach a high degree of importance by the appearance of additional plates so 

 as to form a vault or " tegmen calycis." The anus is situated on the oral surface, which 

 may be bare, or more or less covered by calcareous plates. The water-vascular ring does 

 not communicate directly with the exterior, and the lateral branches of the radial vessels 

 (when present) are respiratory, but not locomotor in function. 



Class 1. Ckinoidea, Miller, 1821. 



Crinoidea, Auctoriuu. 



Stilasteritm, Goldfuss, 182G-1835. 



Ast&rencrinidea, de Blainville, 1834. 



Pinnigrada, Eorbes, 1841. 



Pinnastella, Austin, 1842. 



Brachiata, Burmeister, 1856. 



Actinoidea, Roemer, 1856 (Date, of Preface). 



Encrinidm, Quenstedt, 1876 (Date of Preface). 



Euainoidea, Zittel, 1880 (Date of Preface). 



Definition. — Pelmatozoa, in which the radial plates of the calyx bear more or less 

 branching arms. These consist of segments which are articulated by means of muscles 

 and ligaments, and in most cases bear similar jointed appendages, the pinnules. The 

 nervous system consists (1) of a central organ situated in the calyx, and fibres 

 extending from it through the skeleton of the stem, arms, and pinnules ; (2) of a 

 circum-oral ring and radial extensions which are in close relation with the ciliated 

 epithelium of the ambulacral grooves. These are more or less extensively distributed 

 on the ventral surface of the disk, arms, and pinnules ; and are bordered by groups of 

 tentacles which alternate on opposite sides. When they are absent, the radial water- 

 vessels give ofi" no tentacular branches. The water- vascular ring opens by five or more 

 water-tubes into the body-cavity, which itself communicates with the exterior by a 

 (corresponding number of water-pores. The mouth is central, except in one genus, and 

 the anus subcentral or excentric. The genital glands are lodged in the lower parts of 

 the arms, but are usually fertile only in the pinnules. 



Remarks. — Various writers have attempted at difli"erent times to separate the Crinoids 

 and their allies from the remaining classes of the Echinoderms by somewhat more definite 

 characters than those which distinguish these various classes intei- se. Very little was 



