38 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



Thalassometridae. The proximal syzygies have 19-29 septa, with the degree of 

 strength 2-3. In the Ptilometridae (here included as a subfamily of the Thalassome- 

 tridae) the areola is indistinct, whereas in the Thalassometridae it is generally broad 

 and stout. Very often a concentric furrow appears parallel to the margin of the 

 ossicle. The septa are sometimes forked. There are 1 or 2 indistinct ventral beams. 

 The proximal syzygies in Ptilometra (Ptilometridae) and even in Asterometra (Astero- 

 metridae) are often irregular, sometimes also replacing synarthries. The distal inter- 

 syzygial interval is 5-10 (in exceptional cases 4-18) muscular articulations. 



Charitometridae . The proximal syzygies have 15-22 septa, with the degree of 

 strength 1-2. The areola is usually indistinct. There are 2 ventral beams, more or 

 less indistinct. The complete septa are rather few. Irregularities in the distribution 

 of the proximal syzygies are usual, these often replacing synarthries. The distal 

 intersyzygial interval is 5-10 muscular articulations. 



Notocrinidae. The proximal syzygies have about 20 septa, with the degree of 

 strength 2. Beyond the narrow areola is a broad and almost smooth area. Syn- 

 apticulae occur. Most of the septa reach to the large nearly smooth area, and to 

 the areola. The distal intersyzygial interval is 4-10 muscular articulations. 



Antedonidae. The septa of the proximal syzygies have 11-24, and in the very 

 large Heliometrinae 27-39, septa; the degree of strength is 1-3, reaching 4 in the 

 Heliometrinae. The areola is lacking or indistinct except in Heliometra, in which hi 

 full-grown individuals it reminds one somewhat of the conditions described in Noto- 

 crinus. Rows of tubercles occur only in the Heliometrinae. There are many com- 

 plete septa, these being usually more than half the total number. The distal 

 intersyzygial interval is 2-4 muscular articulations. 



Pentametrocrinidae. The proximal syzygies have 11-18 septa, with the degree 

 of strength 1-3. There is no areola. Half, or even the majority, of the septa are 

 complete. The distal intersyzygial interval is 2-6 muscular articulations, and is 

 rather irregular. 



Atelecrinidae. The proximal syzygies have few septa, not more than 12, with 

 the degree of strength 2-3. There is no areola. The septa are generally complete, 

 sometimes finished, and more or less like tubercles. The distal intersyzygial interval 

 is 2-7 muscular articulations. 



MOVABLE LIGAMENTARY UNIONS IN THE STALKED CRINOIDS 



In the pentacrinites the ligamentary articulations are generally immovable, and 

 more or less pronouncedly synostoses. In the division series and in the first brachial 

 ligamentary union, however, evident indications of synarthries are sometimes present. 

 This is the case in Hypalocrinus naresianus and in the species of Neocrinus. In 

 Neocrinus decorus the distal synostoses seem to indicate a development from this 

 toward the trifascial type of articulation. 



The latter is typically developed in certain bathycrinids, such as Ilycrinus car- 

 penterii, Bathycrinus aldrichianus, and B. australis. In Rhizocrinus lofotensis, as 

 Sars showed and as Gisl^n confirmed, there is a form of loose synostosis in the liga- 

 mentary articulations. In Democrinus rawsonii there seems to be a type intermediate 

 between a synarthry and synostosis. The Phrynocrinidae and Hyocrinidae lack 

 movable ligamentary articulations. 



