1915.] NATURAL SCIENCES OF PHILADELPHIA. 83 



genera with well-developed, quadrangular dorsal and ventral arm 

 plates and the other those with more or less rudimentary dorsal 

 and ventral arm plates. The first group, including littoral forms, 

 is again divided into two sections, one of which, including Ophio- 

 thyreus, Ophiozona and Ophiolepis, is characterized by the presence 

 of a distinct trio of plates just outside and between each pair of 

 radial shields and by the presence of two tentacle scales, which are 

 oval in common outline; while the other, including Ophioceramis 

 and Ophioplocus, is characterized by the absence of a distinct trio 

 of plates just outside and between each pair of radial shields, and 

 by the presence of three to five tentacle scales, which surround the 

 pore. The distinction of Ophiolepis and Ophiozona from each other 

 depends upon the presence or absence of supplementary dorsal arm 

 plates. From a certain point of view, I believe that Ophiozona is 

 more closely allied to Ophiolepis than to Ophiozonella. Ophiozona 

 is found in the West Indies and on the Pacific side of Panama. The 

 faunae of the two sides of Panama stand in a very intimate relation 

 to each other. The distribution of Ophiozona and that of Ophio- 

 derma are equally interesting as illustrating this truth. 



Family 2. OPHIOLEUCID^ nov. 



(Characters as given in keys, pp. 74 and 75.) 

 This family includes Ophiopcepale, Ophiocirce, Ophioleuce,'' Ophio- 

 pallas, Ophiotrochus, Ophiernus and Ophiopyren. 



Family 3. OPHIODERMATID^ Ljungman, 1867. 

 (Characters as given in keys, pp. 74 and 75.) 



Key to suhfamilies of Ophiodermatidce. 



A — Arm spines rather long, not appressed; distal vertebrae some- 

 times imperfectly divided into halves by a series of pores, 



Ophiarachnin^. 

 A A — Arm spines very short, appressed; vertebrae always entire, 



Ophiodermatin^. 



Subfamily 1. OPHIARACHNIN^ nov. 



(Characters as given above in key.) 



This subfamily includes Ophiarachna and three new genera, 

 Ophiuroconis, Ophiurodon and Ophiurochceta. 



'' Ophioden charischema H. L. Clark, 1911, and 0. brevispinum H. L. Clark, 

 1911, are, in my opinion, referable to Ophioleuce. 



