No. 1634. AXIAL CANALS OF RECENT PENTACRtNITIDJE CLARK. 89 



former, only 40 mm. in total length, with (ten) arms 25 mm. long, arc 

 indistinguishable from those in fully mature specimens. The infra- 



8 



Fig. 5. — La ieral 

 view of an - iso- 

 lated infrabasal 

 of isocrinds deco- 



RUS OR METACRI N s 

 ROTUNDUS, SHOW- 

 ING THE FURROW. 

 WHICH FORMS HALF 

 OF THE CANAL CON- 

 TAINING THE PRI- 

 MARY AXIAL CORD. 



Fig. 6. — The infrabasals 

 of [socrinus dbcoros ob 

 metacrinus h t 1 n d d s 

 spread outward, show- 

 ing the course of the 

 furrow's along their 

 apposed sides. 



FiQ. 7. — The CIRCLET 



OF INFRABRASALS OF 

 ISOCRINUS DECORUS 

 OR METACRINUS BO- 

 T U N I) I s. SHOWING 

 T II E APERTURES BY 

 WHICH THE P R I - 

 MARY AXIAL CANALS 

 LEAVE THE CIRC1 E i 

 OF INFRABASALS TO 

 ENTER THE P.ASAI.S. 



basals in the very small specimen just mentioned (the stem of which 

 distally still retains its larval Antedon-like character ) arc in shape 



Fig. 8. — A basal of Iso- 



CRINUS D E C B U S OR 

 METACRINUS ROTUNDUS 

 VIEWED FROM THE INNER 

 END, SHOWING THE SIN- 

 GLE APERTURE BY WHICH 

 THE PRIMARY AXIAL CORD 

 ENTERS FROM THE CIR- 

 CLET OF INFRABASALS 

 AND THE TWO APERTURES 

 BY WHICH THE TWO 

 BRANCHES LEAVE T II E 

 BASAL AND ENTER THE 

 RADIALS. 



Fig. 0. — The same basal, 

 ground down to the 

 plane passing through 

 the center of x ii e 

 three apertures to 

 show the course of 

 the canals and the 

 transverse c n n e c- 

 tive within the ba- 

 SAL. 



ig. 10. — The same BA- 

 SAL, V I E w i: D VEN- 

 T B A I. I. V I DISTALLY), 

 SHOWING THE CWO 

 APERTURES BY WHICH 

 THE TWO BRANCHES OF 

 THE PRIMARY AXIAL 

 CANAL LEAVE THE BA- 

 SAL AND ENTER TWO 

 ADJACENT RADIALS. 



and proportions like those of the adult, though the basals are very 

 short, and the radials much elongated. 



The chambered organ in Isocrinus decorus and in Metacrinus 

 rotundus lies within the dorsal part of the ring of infrabasals; the 



a Dr. P. II. Carpenter says (Challenger Reports, XI, Zoology, p. 291, 1884) of 

 the stems of young specimens of Pentacrinitidse, "the petaloid markings arc 

 evident from the first, as might be expected; " but in the youngesl specimen of 

 Isocrinus decorus he figures (pi. xxxv, fig. 1), the distal part of the stem lias 

 the appearance of the stem of Rhizocrinus, except for the cirriferous nodal 

 joints. This figure aroused my curiosity, and, on examining the original, I 

 found that my suspicions were well founded. I have since been able to dissect 

 part of a stem rather younger than that figured by Carpenter, and find (figs. 

 3 and 4) the articulations to consist of a pair of ligament pits separated by a 

 longitudinal central ridge. 



