78 THE ECniNODERMATA. $f> 73, 74. 



ventral surface of the arms and pinnulae, a furrow, over which the soft 

 skin [perisoma) passes in a bridge-like manner/'"^ 



§ 



io. 



In many Echinoidea the buccal cavity is provided with processes point- 

 ing perpendicularly into the interior of the shell, and Avhich are the 

 points of attachment of the masticatory muscles and ligaments. 



This osseous circle is most developed in the Echinidae.'" and is com- 

 posed of five processes. Between each of these is a smaller one, corre- 

 sponding to as many ambulacral ones, each of which is perforated by 

 a large opening.^'-' In the Clypeastridac. there are five simple processes 

 only;^^^ and in the Spatangidae they are wholly absent. - 



The sub-cutaneous osseous ring about the oesophagus, in the Holothuri- 

 oidea,' corresponds probably to this circle. Usually composed often pieces, 

 it may be regarded as a rudhuentary internal skeleton, for it is the point 

 of attachment of both muscles and tentacles. 



In Holothuria tiihdosa its anterior border is denticulated;^" and in 

 Sy?iapta it is composed of twelve pieces, five of which have oval openings 

 for the free passage of the aquiferous canals. ^^> 



§74. 



The general envelope of many Asteroklea is more or less covered with 

 various calcareous productions. These have the forms of lamellae, knobs, 

 callosities, granules, immovable rays both sharp and blunt, rough and 

 smooth movable points, double hooks, &c."' 



In the Echinoidea, there are points of very variable size united to 

 knobs which are scattered over the external surface of the shell. These 

 points project through the thin skin covering this shell, having at their 

 base a kind of capsular articulation.'-^ 



Remarkable cutaneous organs are found in Synapta. These are small 

 anchor-like hooks, by which these animals attach themselves to objects. 

 Each of them is obliquely inserted under a small sub-cutaneous scale, 

 which is perforated by a canal. '^^ 



10 In the Crinoidea, as well as in the Echino- bristled points, project from the surface of So- 



derms generally, the parts of the skeleton have a taster and C/iaetaster. With Ophiocoma and 



calcareous, r^jticulated structure ; see Miiller^s Ophiomastix, the margins of the arms are covered 



Arch. 1837, p. 9o, and Ueber d. Bau. d. Pentaori- with smooth points, which in Opiiiutkrix are 



nus caput Medusae, in the Abhandl. d. Berl. Akad. spinous. In Ophionyx these spinous iioints have 



1841, i'af. I. fig. 3. movable double hooks ; see the beautiful figui-es 



1 Echinus, Cidaris. of Mklier and Troschcl (System d. Asteriden). 



2 f^aleutin, Monogr. Inc. cit. PI. II. fig. 15. - Tlie spina's of the Echinoidea have, over their 



3 Asiossiz, Monogr. d'i;chinoderm>;g, 2 le LivT. wliole e.xteut, nmnerous, denticulated ribs ; see 

 containing the Scntellal, PI. XIII. fig. 3, PI. Valentin, Monogr. loc. cit. PI. III. fig. 26. la 

 XXVII. fig. 7 (Lobophoru and Echinocyamiis). Spatangus the spines are spatulate, and in the 



4 Tiedeinanu, Anat. d. BOhrenliolothurie, &c., C'iypeastridae (Mellita, Encope, La^anum) they 

 p. 26, Taf. II. fig. 5 ; also Wagner, Icon. zoot. are clavate. The minute researches of Valentin 

 Tab. XXXII. fig. 15. (Monogr. loc. cit. p. 24, PI. Ill) have shown the 



Koreti has observed that the osseous ring is structui-e of the spines of the Echinoidea to be very 



composed of ten pieces with Thyone fuscus and comple.x. 



Ctivieria sqnam'ita of the Hololhurinae. s The burr-like roughness of the skin of Synapta 



6 Quatref'ag'cs, Ann. d. Sc. Nat. XVII. 1842, has already been observed by Esckscholtz (Zool. 



p. 47, PI. iV. Ug. 5 ; PI. V. fig. 7, c. c. Atlas, lift. 2, 1829, p. 12). Jaeser (Oe Ilolothu- 



1 With Oreaster and Culcita, the whole body is riis dissertatio, 1S33, Tab. I. fig. 3) first figured 



covered wilh kiiiil)3 and granulatias. With As- the c\xta,nco\xs hooka of Synapta Beselii. Qiiatre- 



tropecten and SlKUasler, you lind flattened points fagcs (Ann. d. Sc. Nat. XVII. p. 33, PI. III.) has 



and marginal lamellae. Innumerable rays, with given a very exact description of those of Synapta 



