86 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



The disk is 12-15 mm. in diameter and is strongly incised. Usually the disk 

 ambulacra are protected by a well-developed calcareous plating that ceases at the 

 arm bases. The anal tube is more or less completely covered with coarse calcareous 

 concretions. The other interambulacral areas may contain more or less numerous 

 plates, or they may be naked. 



Color in life. Dr. H. L. Clark says that the color is primarily a reddish purple or 

 even deep claret with the dorsal surface of the arms more or less yellow, but the 

 amount of yellow varies enormously; at one extreme are individuals that are practi- 

 cally all purple, really unicolor, and they are not rare, while at the other are those in 

 which the yellow predominates to such an extent that only the tips of the cirri and more 

 or less of each pinnule distally are purple. The most beautiful specimens are yellow 

 or nearly white, finely speckled more or less profusely with purple. In preserved 

 material, even that which has been very carefully prepared, the yellow shades become 

 buff or light brown, and the purple becomes dingy and often distinctly brown. Natu- 

 rally such museum material fails to give any adequate idea of the beauty of the living 

 animal. 



The largest specimen taken by Dr. Clark, from Roebuck Bay, was deep claret 

 with the dorsal side of the arms yellow; some of the young arms were tipped with 

 white. As preserved it is a deep purple, and only distally do the arms show that they 

 were dorsally yellow in life ; they are now a light brown dorsally near the tips. The 

 cirri are dark purple, a few of them cream color near the base. 



Notes. One of the two specimens from northwest of Heirisson Prong, Shark 

 Bay, is the finest example I have ever seen of this species. It has about 100 arms, 

 which are 130 mm. in length. The IIIBr series are mostly 2, but all the other divi- 

 sion series are 4 (3+4). The cirri are about XXXV, 47-54, from 50 mm. to 55 mm. 

 long; dorsal spines begin to develop from the seventeenth to the twentieth segment. 

 The color is deep purple. 



The other specimen is rather small, with about 65 arms which are about 85 mm. 

 long. The IVBr series are usually developed internally in reference to the IIIBr 

 series. The cirri are composed of 37-45 segments and are from 25 mm. to 30 mm. 

 long. 



The specimen from South Passage, Shark Bay, has 50 arms 140 mm. long; the 

 cirri are about XXXV, 30-31, stout, 25 mm. in length. One IIBr 2 in a IIBr 4(3+4) 

 series bears instead of a pinnule a slightly undersized arm the first division series of 

 which consists of 5 ossicles all apparently united by synarthry and none bearing 

 pinnules. This division series carries two IVBr series, both of which are 4(3+4). 

 The arms have a knotty and irregular appearance which is probably due to parasitiza- 

 tion. P! is from 23 mm. to 25 mm. long, very stout basally and tapering gradually 

 to a delicate tip, and is composed of from 25 to 27 segments. 



Dr. H. L. Clark collected 20 specimens of this species at Broome and 5 at Lagrange 

 Bay of which, he said, the most interesting are the largest and the smallest. The 

 smallest, from Lagrange Bay, has 19 arms 20-25 mm. long; the 12 division series 

 beyond the IBr series (which would give 22 arms) are all 4(3+4); the cirri are XIII, 

 25-29, relatively very long, more than half as long as the arms. The color is uni- 

 formly deep purple. Dr. Clark says that in spite of its small size it is quite a typical 

 microdiscus. The largest specimen, in its present dry condition very nearly 300 



