158 LOWER INVERTEBRATES. 



crowned with small tufti'il sjiim's called paxilli. They are nmst iiuiiieruus in the hot 

 seas. 



The genus Aatroj'&'ttii is a large one, anil many species occur in deeji water. A. 

 articulatus ranges from New Jersey to the West Indies. Several s]iecies are known 

 to occur ou the west co.ist of Xorth Amerii-a. 



Nearly allied to Astropecte/i, hut differing from it in the \ery cousjiicuous feature 

 of the ahsence of any large marginal plates on the sides of the rays, is Ijuidia^ the 

 hrittle star-fish, celebrated for its power of breaking into fragments when it is brought 

 from the bottom. L. chttlwiitu ranges from New Jersey to the West Indies, and is 

 common in the C'arolinas. L. tcstielluta, a tine species, attaining a diameter of more 

 than a foot, ranges from the (-iulf of California to Peru. < 'hnodincnK i-rispati(s is 

 another North Atlantic sjiecics, ipccuning in the North Sea, (ireenlan<l, and New Eng- 

 land. It is almost pentagonal from the sliortniss of the rays. 



X,eptij(;lKistrr keiyueleneitsis has its tloi'sal surface covered with a tessellated pave- 

 ment of paxilli oi- s])ines, with large heads. These paxilli form with their approxi- 

 mated heads a sort of hexagonal mosaic on the surface, but Ijetween their slender 

 shafts arcade-like sjiaces are left, and into these spaces the eggs ])ass from the genital 

 openings. Eggs and young in all the eal'ly stages of development occupy the.se spaces 

 at once, but when at least six siu'kers have formed ou each arm, they push their way 

 out between the paxilli. usualh iu the angles lietwiTU the arms. The young escajie 

 mouth u}i]ierinost, and ilisengagc tlu^ir .arms one liy one. .Vfter this they rem.ain at- 

 tached to the parent for some time, iu the young, the madreporic plati' can be seen 

 near the margin of the disc, but in the adult it is hiddi'u by tlu' paxilli. 



Arc/taster re.nU lifer, taken in tliiee iiuudreil and forty-four fathoms, west of the 

 Shetland Isles, is a tine s|iecies .ibciut ten inches across, remarkalile for the arrange- 

 nu'Ut of the ambulacral s|iiiies, wliicli foian coiiibs that increase iu size toward the 

 base of the arms. Ka<-h |ilatc li.-is a doulile row uf spines, and eacli spine has a 

 second short sjiine at its end. 'i"he anib\daci-:il ^■l•oo\ es .are much wider, and the 

 ambulacral tubes larger in pro]iortion to the aiiinial than is usual. 



Archaster bi/rons, taken in deeji water noith of the Hebrides, nu'asures five inches 

 across, and is of a rich cream or light rose tint. 



PorreUanaster rarnJnitit was dredged by the 'Challenger' in one thousand two 

 hundred and forty fathoms, in the Gulf Stream. The arms are rather shorter than the 

 diametei- of the disc; the ambulacral pl.ates ai-e lai-^c. and fiuMiished with two flat- 

 tened S]iines; and the jilates forming the .angles of the mouth .■n-e unusually flattened 

 and expanded. There are two rows of large marginal jjlates, and the two on the end 

 of each arm are fused together, and bear three spines, one on each side below, and a 

 central one above. Vertical rows of small flattened scales cover the two central 

 ]iairs of marginal plates in the re-entering angles between the arms, and look like a 

 little brush between each pair of arms. The upper surface is eovei'ed with narrow 

 calcareous plates, and is of a delicate cobalt blue color. The excretory opening is 

 very distinct in the centre of the disc. It h.-is been found in the North Pacific and 

 near Tristan d'Acunha. 



The AsTERiNiDJi are pentagonal, more ox less elevated in the centre of the disk, 

 and always sharp at the edge. Spines are present, at least on the ^■eutral surface, and 

 there are two rows of pedicels in the ambulacral grooves. 



Asteropsin imhricata, a species which ranges from Vancouver's Island to near San 

 Francisco, is a good examjile of this family. The skeleton of the aboral side is a retic- 



