186 ZIESENHENNE 



with only 3, one Atlantic, one Pacific, and one in both Pacific and Atlan- 

 tic, being reported from deeper waters. 



To help future workers on this group, a key is given to all the ac- 

 cepted species, with the literature and distribution for each. Only the 

 Pacific species are discussed in greater detail. 



Genus OPHIODERMA M. & T. 



Ophioderma Mliller und Troschel, 1842, Syst. Ast., p. 83, 86. 



Ophiocryptus (partim) H. L. Clark, 1915, Jour. Entom. Zool., vol. 7, 

 no. 1, p. 64. 



Diagnosis: Differs from the other genera of the family Ophioderma- 

 tidae in having four interradial genital slits confined to the underside 

 of the disk, arms twice the length of the disk diameter, and flat disk 

 plates. 



Type species: Asterias longicauda Retzius 1805. 



Remarks: There are two other genera in the family Ophioderma- 

 tidae which have four genital slits, Ophioncus Ives and Ophiocryptus 

 H. L. Clark. The former, however, has arms barely the length of the 

 disk diameter, while the latter has large convex disk scales. Both are 

 monotypic and restricted to California waters, and range northward 

 beyond the limit of Ophioderma. The three species of Ophiocryptus 

 described by H. L. Clark and Nielsen are now considered juvenile stages 

 of Ophioderma. 



KEY TO THE SPECIES OF OPHIODERMA 



1. Upper arm plates divided into numerous smaller plates ... 2 



1. Upper arm plates not divided into numerous smaller plates . . 8 



2. Radial shields completely covered 3 



2. Radial shields normally exposed, sometimes partly covered in 

 longicaudum and teres 4 



3. Distal margin of under arm plate bi-lobed, heart-shaped. Lo- 

 cality doubtful: East Indies 



1. pr pinquu7n* yiothler 

 3. Distal margin of under arm plate convex. West Indies . . . 



2. guttatum Liitken 



