ClDARID^E.- 



-RADIATA.- 



-AsTEROIDEA. 



393 



and this is covered with a series of vibratile cilia. 

 Tliese organs, as Mr. Gobse observes, are so unique 

 in their forms and functions, so apparently inde- 

 pendent of the animal's will in their movements, 

 that it was long a matter of dispute whether they 

 were truly organic appendages or merely parasitic 

 intruders. The family is well represented in Plate 2, 

 figs. ], 2, ?j, 4 — li? 2^Eckinus miliaris ; fig. 3, Echinus 

 e/cif'nis ; fig. 4, Eclduiis sardtcus ; and fig. 1, Ecliino- 

 vielra maninullatits. 



Family II.— CIDARID^ {T/tc Diadnns). 



This family is distinguished from the Echinidse by 

 having the tubercles to which the spines are affi.xed 

 pierced with a central pit. Through this perforation 

 a small muscle passes, which is attached to the spine, 

 and by means of which it is moved. The shelly case 

 is globose, the ambulacra continuous from mouth to 

 anus, and the spines are of several forms. The family 

 is divided into a considerable number of genera, and 

 contains many species. It is represented in Plate 1, 

 fig. 2, by Diadcma Jistularis, exhibiting the spines 

 with which the case is covered; fig. 1, Astropyga 

 radiata, with the spines removed to show the structure 

 of the shell ; and fig. 4, Cidaris iinperialis. 



Family III.— SCUTELLID^ {The Calce-wxldiis). 



The Cake-urchins have a thick, pentagonal shell 

 composed of twenty bands of pieces, like the Echinida;. 

 It is elliptical or circular, and covered with small, luii- 

 form bristles. This crustaceous covering is usually 

 thickened internally by an additixjnal coat, and is 

 strengthened by internal columns, which enable these 

 brittle-looking shells to resist the action of the sea for 

 a length of time. The ambulacra are formed of single 

 series of double bores, forming petal-like impressions 

 on the dorsal surface ; wliile on the under surface there 

 are peculiar ray-like furrows going out from the centre 

 and ramifying all over it. The vent is posterior, and 

 placed near the margin. The mouth is five-sided, and 

 the jaws are composed of five horizontal plates. This 

 family is represented in Plate 3, fig. 1, by Eclanan- 

 thiis (Clypeaster) suldepressus ; fig. 2, Aracknoidcs 

 placenta ; figs. 3, 4, Rutula Awjusti. 



Tamily IV.— GALERITIDiE. 



The shelly case in this family is thin, elongate or 

 eub-circular, or sub-conic, and is covered with very 

 fine bristle-like spines set on very close, small tuber- 

 cles. The mouth is central and destitute of jaws. 

 The vent is inferior and placed on the posterior mar- 

 gin. The ambulacra are arranged in a single series of 

 double pores. The body, like the Echinidae, &c., is 

 formed of twenty vertical bands, the ambulacra! bands 

 being the narrowest. The family is represented on 

 Plate 4, tigs. 1, 2, by Galcritcs albo-galcrus, a fossil 

 epecies; and figs. 3,4, by Ecliinoneus minor. 

 Vol. II. 



Family V.— ECHINOLAMPASID^.. 



The shell in this family is elongate or sub-circular 

 and covered with very small, uniform bristles, which 

 are set upon small tubercles that are scattered oi 

 placed in series. The mouth is central, or rather in 

 front of the centre, and is destitute of jaws. The vent 

 is posterior, dorsal, or inferior ; and the ambulacra are 

 formed of two series of double pores. The fanjily is 

 represented in Plate 3, figs. 7, 8, by Cassididus Caribie- 

 arum ; Plate 4, fig. 5, by the fossil species Echinolam- 

 pas K'dnigii; and fig. 6, Echinohrissus Breynii, also 

 fossil. 



Family VL— SPATANGIDiE {The Heart-urchins). 



The shelly covering in this family is thin, elongate 

 or sub-circular, with an anterior dorsal groove, gene- 

 rally heart-shaped, and like the other Echinoidea, 

 formed of twenty bands of pieces. It is composed of 

 large polj'gonal plates, few in number, and is covered 

 with crowded, uniform, hair-like spines, with larger, 

 longer ones placed on perforated tubercles, and band- 

 like fascicles covered with very short, minute spines. 

 The vent is terminal, and rather above than below the 

 terminal border. The ambulacra are short, petal- 

 shaped, and are only four in number. This family is 

 represented in Plate 4, figs. 12, 13, by Brissus ventri- 

 casus ; and figs. 9, 10, by Schizastcr Alropos. 



Ordek II.— ASTEROIDEA {Star-fishes). 



The Star-fishes, or Sea- stars as they are often 

 called, differ considerably from the previous order in 

 many respects. Instead of having the soft parts of 

 the body covered by a hard, calcareous case, the Star- 

 fishes have them protected by a coriaceous, leathery, 

 or cartilaginous skin, strengthened by calcareous plates 

 imbedded in its substance, and in which are implanted 

 spines or tubercles. The body is expanilcd into a 

 series of arms, generally five in number, frequently 

 more, varying from eight to thirty, and of the same 

 structure as itself. The under surface of these arms 

 is marked with gutters or grooves proceeding from 

 the mouth in the centre of the disc to the very tip, 

 and which are called the ambulacra or avenues^ 

 answering to the same parts described by that name in 

 the Echini. These gutters are pierced, as in these ani- 

 mals, with several rows of small holes, through which 

 issue tentacula with expanded tips capable of contract- 

 ing and elongating themselves. It is by means of these 

 tentacles, acting as suckers, that tlie animals are enabled 

 to walk. The mouth of the SUir-Cshos is always placed 

 in the inferior centre of the rays. This leads to the 

 stomach, which is in form of a bag, and which pos- 

 sesses only one aperture, through which the food is 

 received and the indigestible part rejected. From this 

 stomach two branched ca;ca extend to each ray. The 

 food of these animals consists of young shells, small 

 Crustacea, and other marine creatures. They have the 



3D 



