562 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



In one of these there is no trace of cirri, the anal plate separates two of the 

 radials, and there are two short brachials. 



There are five discoidal segments at the tap of the broken column, which is 

 much more robust than that of the corresponding stage of Antedon bifida, while 

 the crown, which is 1.1 mm. in length, is nearly twice as large as that of Antedon 

 bifida. 



The orals, which rest directly on the radials, were compared by Carpenter to 

 those of Hyocrinus, having a deep median groove, which is more marked than 

 in that type, with the lateral borders folded over somewhat strongly. This 

 character is more pronounced than in the larva of Antedon bifida. 



Carpenter notes that this pentacrinoid, which. Like the succeeding, was deter- 

 mined as belonging to Hathrometra prolixa by a process of elimination, resembles 

 the larva of H. sarsii in the great height of the basals but differs from it altogether 

 in the unusual shortness and width of the radials and IBr series. 



In the second larva the column, which is broken about 20 mm. from the 

 calyx, forms an attachment to a hydroid tube at about its thirtieth segment, and 

 is continued downward for half a dozen segments further. 



There are six discoidal segments below the rudimentary centrodorsal, which 

 bears the sockets of five short cirri, only one of which remains, reaching to the 

 distal border of the basals, which collectively make up about half the height 

 of the cup. 



The IBrj and IBr, (axillaries) are well developed, as are also the arms, 

 which are broken at about the tenth brachial or earlier; but even under these 

 circumstances the crown has a length of 4 mm. 



A slightly bifid plate ha-\ang a somewhat worn appearance stands up in one 

 of the interradii of the disk. Carpenter states that it may be one of the orals, 

 but is more inclined to regard it as the radianal. 



A striking feature of this very robust larva is the large development of 

 the arms before the appearance of the cirri. The radials and brachials are larger 

 than those of a recently detached Antedon bifida. 



The brachial ambulacra of this larva are protected by relatively large plates 

 not unlike those in certain forms in the genus Leptometra, though the armature 

 of the ambulacra in the adult H. prolixa consists of quite simple carcareous rods. 

 This difference, as stated by Carpenter, may perhaps be explained by an 

 absorption of the perisomatic skeleton of the pentacrinoid, such as seems to take 

 place in certain forms of Antedon. 



In addition to many of the specimens described by Doctor Mortensen I have 

 personally examined the following: 



East of Jan Meyen (lat. 72° 05' N.. long. 0° 36' W.), 96 fathoms; taken on 

 July 24, 1891. 



A well-developed example in a poor state of preservation. 

 East of Iceland (lat. 65° 00' N., long. 11° 16' W.), 310 fathoms. 

 The radials are in contact laterally through the rather broadly truncated 

 lateral angles. 



Northeast of Iceland (lat. 67° 53' N., long. 10° 19' W.). 1.010 fathoms. 



