A MONOGRAPH OF THE EXISTING CRINOIDS 37 



Summary 



Gislen said the author's statement that the number of syzygial septa is "to a 

 certain extent proportionate to the size of the articular face, and is greater in the 

 Oligophreata than in the Macrophreata" in general holds good. But there are some 

 important exceptions, especially to the latter assertion. For instance, the oligophreate 

 families Calometridae and Charitometridae have unusually few septa, and the same 

 is true in regard to most of the Thalassometridae and certain of the Colobometridac. 



Comasteridae. — The septa in the proximal syzygies are usually numerous (30-58), 

 below 20 only in small forms. The degree of strength is 3-4. The areola is strongly 

 developed, but rather narrow. Plenty of tubercles occur, often also ventral tubercle 

 rows. Pseudosyzygies sometimes appear among species of the genus Comaster 

 between the first two post radial ossicles (the elements of the IBr series). These, 

 like typical syzygies, often replace synarthries. The distal intersyzygial interval 

 is normally 3-4 muscular articulations (an exception in Capillaster). 



Zygometridae. — There are 16-30 septa in the proximal syzygies. The degree of 

 strength is 2-3. The areola is indistinct. A syzygy replaces the most proximal 

 synarthry. The young stages of these syzygies often remind one of the pseudosyzy- 

 gies in Comaster. The number of incomplete septa is large. The distal intersyzygial 

 interval is fairly short, 3 muscular articulations in Eudiocrinus (now assigned to a 

 special family, Eudiocrinidae) , and 4-8 in Catoptometra. In Zygometra, however, 

 the interval is long, 10-30 muscular articulations. 



Himerometridae. — In the proximal syzygies the septa number 35-50, with the 

 degree of strength 2-3. The areola is indistinct. Sometimes there are 2 clearly 

 marked ventral beams. The number of incomplete septa is rather large. The distal 

 intersyzygial interval is long, (6) 10-26 muscular articidations. 



Mariametridae. — The proximal syzygies have 25-40 septa, except in the delicately 

 built genus Mariametra in which there are only 15. Gislen remarked that the heavily 

 granulated disk also shows Mariametra to be a primitive type. The degree of strength 

 is 2-4. The areola is well developed — in Stephanometra narrow but distinct. There 

 are 2 ventral beams. Complete septa are few. There are occasionally incidental 

 irregularities in the distribution of the proximal ligamentary unions, so that syzygies 

 may replace synarthries. The distal intersyzygial interval is fairly long, 5-18 muscu- 

 lar articulations. 



Tropiometridae. — The septa in the first syzygy number about 50, with the degree 

 of strength 4. The areola is stout, raised on a conical prominence. There are a good 

 many complete septa. The distal intersyzygial interval is 5-10 muscular articulations. 



Colobometridae . — The proximal syzygies have 15-30 septa, with the degree of 

 strength 2-3. The areola is narrow, distinct or indistinct. There is rather a large 

 number of complete septa. There is great diversity within this family, Cenometra 

 reminding one of Liparometra, Oligometrides of Tropiometra, Cyllometra of the ante- 

 donid type, and Austrometra most nearly of certain Thalassometridae. The distal 

 intersyzygial interval is 3-10 muscular articulations. 



Calometridae. — The proximal syzygies have 13-19 septa, with the degree of 

 strength 2-3. The areola is broad and stout. There are few complete septa. The 

 distal intersyzygial interval is 3-15 muscular articulations. 



