14(5 LOWER (NVERTEBRATES. 



Tho most pomnion pcntacrinoid of the Cnrihhonii Sens is n]i]iarently P. flecorus, in 

 which the whole of the cirri are separated hy ten to twelve internodal joints; the norlal 

 joints ai'e lari^v ami jirojectino:, and the two outer radials, and the first two joints 

 Vx'yond them -aw united hy ligament, instead of liy niusries or by a sy/.ygy. 



/'. hiiilleri, thciuii'li confoun(le(l with this species liy Tiiomsoii, differs widely. 

 The internodal joints of the stem, are nnly si\ or eigiit ; the cirri are stout, and have 

 about forty joints, the outer radials and succeeding joints are united by syzygy, as 

 in -/-". asterlii, and the amis foi'k inucli as in the latter. Eight sjiecies oi Peiitacrintis 

 .are now' known. 



The most wi<lely distriliuted, and at the same time one of the simplest of living 

 crinoids is lihizocrinus /o/blends, a species which does not exceed three inches in 

 length, and lives at depths of from one hnndred to one thousand fathoms in the North 

 Atlantic, and upon the coasts of Florida. The stem is relatively long aii<l many- 

 jointed, some of tlie basal articulations bear Ijranched, root-like lilameiits, or cirri, and 

 •at its summit is a calyx consisting of a central jiiecc or basal and five first radials, all 

 closely united together and |ierclied ii]ion the eiilargcil solid, peai'-sliaped iip]ier joints 

 of the stem. To these five first radials, follow two otlicr series of radials, all included 

 within the calyx, but each following the line of an arm. To lli<- third i-adials are 

 attached the first of the ossicles of the unbianclu-d liut piinuile-lie.-iring arms, which 

 vary in number from four to seven, and lia\c from twenty-eight to thirty-four joints. 

 The pinnules alternate with each other along the .arms, and lia\c also a jointed skele- 

 ton. The mouth is eircailar, but is surnumded by the live (m- four) oral valves, which 

 chise over it wjien siiut. Between the eiicular li|i and the oial valves there is a serie.s 

 of soft, flexible, tentacles, two p.airs to each \ alve. The outer one of each pair is very 

 contractile. Tentacles of a similar cluu-acter are coutiinied along the deep grooves 

 which traverse the oral surface of the arms and j'innules. 



Ji. rairsoni is readily known from the last species liy its more robu.st appearance 

 and elongated calyx, which is nearly always constrict (■<! .it the suture with the radials. 

 The greater part of the eu]i in this genus is formed by tiie clongatetl basals, which, in 

 the Norwegian variety of R. lofotensis are so completely fused that no sutures are 

 visible, a peculiarity which led to the .sujiposition that this ]iart was formed of enlarged 

 upper stem-joints as in a <_'oiiiiitiiIii. li. niirso/ii is .a larger form than Ji. lo/otensits. 



Hj/ocriirus f'c//icniiniHt< ]\:\s univh the stiMicturc of the \r.\]:vozoii.' J'htti/vrliins. It 

 has a rigid .stem made up of cylindrical joints applied to each other by .a close syzygial 

 suture. The cup consists of a basal ring winch seems to be f(n-med of two or three 

 pieces, and of a tier of fine, thin, l)road, spade-sha)ied radials. The arms are live in 

 number, and arc built uji of long, cylindrical joints. The lir>i. tlirce joints consist of 

 two parts se))arated by a syzygy, the other joints h.ave two .syzygies. P'rom the tiiird 

 and all subsequent joints springs a ])innule, the pinnules alternating on either side of 

 the arms. 'I'he lowt'st ]iiiiiiules are very long, the succeeding ones liecoming shorter. 



The outer part of the disc is paved with irregular closely-set plates, bounding the 

 live large oral valves. The a'sophagns is short, and is succeeded by a stomacli sur- 

 rounded by brown glandular ridges, the intestine is very short, and contracts rapidly. 

 Round the gullet a rather ill-defined oral ring gives off, opjwsite each of the oral plates, 

 a group of four tubuhir tentacles. This s]iecies was dredged near the Crozet Islands, 

 and also with Bathi/crinim, in eighteen hundred and fifty fathoms, off Brazil. 



HoIopKn is a short, stout form with no triu' stalk, with a broad, encrusting base 

 instead of the bnmching cirri oi Iilii7,oci'inut>, and ten arms which can be rolled together 



