.'Is Hi t.I.K I IN 82, l \lli:i) STATES NATIONAL MUSEUM 



ThaiasBometridae. The proximal Byzygies have 19-29 septa, with the degree of 

 Btrength 2 ;i. 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 



le. The septa are Bometimes forked. There are 1 or 2 indistinct ventral beams. 

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

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

 Byzygial interval is 5 10 (in exceptional eases 4-18) muscular articulations. 



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

 Btrength l 2. The areola is usually indistinct. Tliere are 2 ventral beams, more or 

 Irs-, indistinct. The complete septa are rather few. Irregularities in the distribution 

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

 intersyzygial interval is :> 10 muscular articulations. 



Notocrinidae. The proximal Byzygies 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. 



Aniedonidae. The septa of the proximal syzygies have 11-24, ami in the very 

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

 Beliometrinae. The areola is lacking or indistinct except in Helwmetra, in which in 

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

 crlinis. 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. 



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

 of strength 13. 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 inten al 

 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 s}mostoses. In the division series and in the first brachial 

 ligamentary union, howe> er, evident indications of synarthries are sometimes present. 

 'Phi- is the case in Hypalncrinus uairslanus and in the species of Neocrimis. In 

 Neocrinua deeonu the distal synostoses seem to indicate a development from this 

 toward the trifasciaJ type of articulation. 



The latter is typically developed in certain bathycrmids, such as Ihjcrinus car- 

 penterii, Bathycrinus aldrichianus, and B. awtralis. In Bhizocrinu& krfotensis, as 

 San showed and as Gislen confirmed, tliere is a form of loose synostosis in the liga- 

 mentary articulations. In It, nmcriinis rmrxnitii there seems to be a type intermediate 

 between a Bynarthry and synostosis. The Phrynocrinidae and Hyocrinidae lack 

 movable ligamentary articulations. 



