MONOGRAPH OF THE EXISTING CRINOIDS. 567 



In free-living individuals 1.5 inches in length the same structure, composed 

 of one or two spicules, still persists in each of the ambulacral lappets, and they 

 are found in the pinnules of adult individuals of Antedon petasus from 3 to 4 

 inches in length, although here they are much reduced. 



These spicules also occur in the pinnules, at least in those of the distal half 

 of the arms, of the adult H. sarsii. 



Along the ventral groove of the arms there are two rows of tentacles and 

 two rows of colored vesicles (sacculi). As yet there is only one pair of these 

 for each brachial, though in the adult there are many, usually three pairs. 



The tentacles are cylindrical, with very slight equally spaced constrictions, or 

 feebly annulated, and are furnished with minute tactile papillae which are slender, 

 cylindrical, and rounded at the ends. 



The sacculi, situated on the outer side of the tentacles, are spherical, and 

 opaque reddish yellow or reddish brown as in the adults. In life, however, they 

 are colorless. On the disk there is a pair of them above the base of the IBr^ 



There were four specimens taken at the beginning of March at the Guldbrand 

 Islands, in 100 fathoms, and at Skraaven, in the Lofoten Islands, in 300 fathoms, 

 two of which were attached to the stem of a Rhabdopleura mirabilis, the two others 

 being affixed to the tests of rhizopods. 



The largest of these has a total length of 20 mm., of which the crown (includ- 

 ing the arms) occupies 4 mm. The column is composed of 38 segments. The 

 three others are slightly smaller, from 13 mm. to 16 mm. in length. 



As a result of the development of the digestive organs and of the soft ventral 

 disk which covers them the calyx has become greatly enlarged, and the oral plates, 

 now separated as a consequence of this increase in size from the much enlarged 

 and much further developed radials, are still fairly large but seem from this time 

 onward to become more and more reduced and rudimentary. 



The form of the radials has changed considerably. The distal border, pre- 

 viously short and straight, has become very broad and concave to receive the base 

 of the IBr^ which similarly has broadened. On the distal border of the radial 

 circlet there are now to be seen five rounded-triangular interradial angles with 

 rounded apices which project distally on the lines of the interradial sutures, and 

 are slightly bent inwardly. 



The IBr 2 , similarly enlarged, is almost as broad and high as the IBr^ The 

 arms, considerably elongated, are each now composed of 14 or 15 brachials. In 

 the largest specimen, though not in the others, the arms are bifurcated at the tip. 

 Examining these more closely, it is found that this is in reality the first formation 

 of the pinnules. The pinnules are still very short and filiform, being at the base 

 about half the thickness of the arm and gradually tapering distally. They are 

 composed of a few indefinite segments, of which the two lowest already show 

 sacculi, which, however, are much smaller than those on the arm itself. 



A pentacrinoid in a more advanced stage of development, taken in the middle 

 of April at Skraaven in 300 fathoms, is 21 mm. long, the crown (with the arms) 

 measuring 4 mm. 



142140 21 Bull. 82 38 



