146 LOWER INVERTEBRATES. 



The most common pentacrinoid of the Caribbean Seas is apparently P. decorus, in 

 which the whole of the cirri are separated by ten to twelve internodal joints; the nodal 

 joints are large and projecting, and the two outer radials, and the first two joints 

 beyond them are united by ligament, instead of by muscles or by a syzygy. 



P. mulleri, though confounded with this species by Thomson, differs widely. 

 The internodal joints of the stem, are only six or eight; the cirri are stout, and have 

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

 in P. asteria, and the arms fork much as in the latter. Eight species of Pentacrinus 

 are now known. 



The most widely distributed, and at the same time one of the simplest of living 

 crinoids is Phizocrinus lofotensis, a species which does not exceed three inches in 

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

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

 jointed, some of the basal articulations bear branched, root-like filaments, or cirri, and 

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

 closely united together and perched upon the enlarged solid, pear-shaped upper joints 

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

 within the calyx, but each following the line of an arm. To the third radials are 

 attached the first of the ossicles of the nnbrauched but pinnule-bearing arms, which 

 vary in number from four to seven, and have from twenty-eight to thirty-four joints. 

 The pinnules altei-nate with each other along the arms, and have also a jointed skele- 

 ton. The mouth is circular, but is surrounded by the five (or four) oral valves, which 

 close over it when shut. Between the circular lip and the oral valves there is a series 

 of soft, flexible, tentacles, two pairs to each valve. The outer one of each pair is very 

 contractile. Tentacles of a similar character are continued along the deep grooves 

 which traverse the oral surface of the arms and pinnules. 



P. rawsoni is readilj- known from the last species by its more robust appearance 

 and elongated calyx, which is nearly always constricted at the suture with the radials. 

 The greater part of the cup in this genus is formed by the elongated basals, which, in 

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

 visible, a peculiarity which led to the supposition that this part was formed of enlarged 

 upper stem-joints as in a Comatula. P. rawsoni is a larger form than P. lofotensis. 



Hyocrinus hethellianus has much the structure of the paleozoic Platycrinus. 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 which seems to be formed of two or three 

 pieces, and of a tier of fine, thin, broad, spade-shaped radials. The arms are five in 

 number, and are built up of long, cylindrical joints. The first three joints consist of 

 two parts separated by a syzygy, the other joints have two syzygies. From, the third 

 and all subsequent joints springs a pinnule, the pinnules alternating on either side of 

 the arms. The lowest pinnules are very long, the succeeding ones becoming shorter. 



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

 five large oral valves. The oesophagus is short, and is succeeded by a stomach 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, opposite each of the oral plates, 

 a group of four tubular tentacles. This species was dredged near the Crozet Islands, 

 and also with Bathycrinus, in eighteen hundred and fifty fathoms, off Brazil. 



Holopus is a short, stout form with no true stalk, with a broad, encrusting base 

 instead of the branching cirri of Phizocrinus, and ten arms which can be rolled together 



