498 THE ANATOMY OF INVERTEBRATED ANIMALS. 



present day only by the genera Antedon (Comatula), Acti- 

 nometra, Comaster, Pentacrinus, Rhizocrinus, and Holopus. 



The first three genera are capable of locomotion, while 

 the next two are attached by long articulated steins to sub- 

 marine bodies. Holopus^ which is but imperfectly known, 

 appears to be fixed by a short, thick, unjointed prolongation 

 of its base. 



Rhizocrinus lofotensis (Fig. 146), which has been very 

 carefully and elaborately described by Sars, 1 is a small animal 

 which does not attain more than three inches in length, and 

 lives at great depths (100-300 fathoms or more) in the sea. 

 It consists of a relatively long, many-jointed stem, from many 

 of the articulations of which, branched, root-like filaments, 

 or cirri, are given off ; at the summit of this is seated a cup- 

 shaped body, the calyx, from the margins of which five to seven 

 arms (brachia) radiate. To each arm is attached a double 

 series of alternating pinnulce. The mouth is situated in the 

 centre of that part of the perisoma which forms the surface 

 of the calyx opposite to the stem. The oral aperture is cir- 

 cular, but five (or sometimes only four) triangular lobes of 

 the perisoma, with rounded free ends, project over it, and, 

 when shut, close it like so many valves. From the inter- 

 vals between these oral valves five (rarely four) grooves trav- 

 erse the oral surface of the calyx, and extend thence 

 throughout the whole length of each arm, giving offsets as 

 they go to the pinnules. Thus the oral surface of each arm 

 and of each pinnule is deeply excavated. 



Between the circular lip and the oral valves, soft flexible 

 tentaculiform pedicels are attached in a single series. Two 

 pairs of pedicels correspond to every valve, each pair aris- 

 ing opposite the basal angle of a valve. These pedicels are 

 hollow, their surface is papillose, and the outer or radial pedi- 

 cel of each pair is very contractile. Pedicels of the same 

 general character are continued throughout the brachial and 

 pinnular grooves. 



The anus is situated at the end of a conical prominence 

 between two of the grooves on the oral face of the calyx, and 

 is therefore interracial in position (Fig. 146, III. an). 



The skeleton consists of very numerous pieces resulting 

 from the calcification of the perisoma. In the stem they have 

 the form of elongated, subcylindrical, or hour-glass-shaped, 

 joints (articuli), the opposed faces of which are united by 



i " Memoires pour servir a la connaissance des Crinoides vivants," 1868. 



