18 BTJI.1.KT1N 76, I'NITED STATES NATIONAL MUSEUM 



Tiny have each, however, a long internal process which helps to support or strengthen 

 the dorsal surface (Vide infra). 



The mosl characteristic features of the internal skeleton are the extensive rnter- 

 brachial Beptum; the series of accessory septa extending from the outer end of every 

 second or third ambulacra! ossicle to the border of the abactinal surface; and the 

 comparative distinctness of the odontophore. The interbrachial septum is mem- 

 branous witli parallel dorsoventral columns of elongate, imbricated plates, the inner 

 bonier being concave and strongly reinforced by plates, which are irregular and form 

 a I, and nuieli wider than the other columns. Between the dorsoventral columns 

 there is, in small and medium-sized examples, an area of unfortified membrane, 

 Upon which the plates encroach more and more with advancing age. 



The transverse, parallel septa which are found along the border of the ray are 

 composed of Long blunt processes which grow outward and upward obliquely from 

 the inner surface of the actinal, inferomarginal, and intermarginal plates, the septum 

 being continued dorsally and mesially as a membrance with a free concave mesial 

 border. That part of the septum which joins the abactinal surface is strengthened 

 by keellike extensions of the dorsolateral plates or their lower and outer ends. The 

 condition of these septa, which are pretty evenly spaced, wdl depend upon age and 

 the general "calcareousness" of the specimen. They extend to the end of the ray, 

 becoming smaller as the ray attenuates, and are pretty regularly opposite alternate 

 ambulacra! plates. The ventral processes from the dorsolateral plates are a little 

 more conspicuous in these distal septa. 



The odontophore (pi. 4, fig. (i, 0) is clearly outlined, in most specimens, from the 

 pair of enlarged ambulacra! ossicles which surround the first ampulla pore, whereas 

 in Orthasterias, Stylasterias, and allies, it is hidden by tissue so that its contour is not 

 evident. Its interrndial dimension is about 0.45 of the extreme width. 



The enlarged summit of the first ambulacral ossicle is separated from the 

 companion by a broad muscular suture, oval in form, whose length equals that of 

 the following seven or eight ambulacral plates. 



The ambulacral ossicles are slender and long. The portion which forms the 

 ambulacral ridge is especially compressed and thin, being only half the width of the 

 intervening muscular sutures and therefore narrower than the corresponding part in 

 Orthasterias and allied genera. The ambulacral pores are narrow (on the outside) 

 with flaring sides. There are two rows on either side of the radial line and at the 

 base of the ray the inner ends of the outer row mterdigitate with the outer ends of the 

 inner about one-third their length; far along ray about one-half. The first ampulla 

 pore, <>n the inside, is of conspicuous size. 



Internal <unitt>iit>/. The viscera do not present any differences from the typical 

 AsU Has arrangement. The gonads, of the racemose type, open dorsally on the inter- 

 radial line at about the middle of r. The intestinal coecum is divided into two parts 

 and each of these into about three lobulated subequal divisions, the longest not 

 reaching the middle of r. The spacious stomach has strong retractors and the hepatic 

 coeca are voluminous. The ampullae are obviously single, rather large, and there 

 are conspicuous Tiedemann's glands, but no Polian Vesicles. 



