MONOGRAPH OF JAPANESE OPHroROEDEA. 375 



I will now proceed to the consideration of the Ophiacanthidce- 

 line. As already mentioned, the genera or species with only 

 horizontally flexible arms are a step more archetypal than those 

 with more or less vertically coiled arms ; but the distinction of 

 these two groups can not be very profound, since certain genera 

 include species of both types. As far as the genera examined by 

 myself are concerned, Ophiologimus and OphioUmna are typical 

 representatives of the forms with only horizontally flexible arms, 

 and OphioJehes, Ophiosemnotes and Oph'iochondrella of those with 

 more or less vertically coiled arms. Ophiologimus, as probably 

 also Ophiotoma, OpJiioblenna, Ophiomyces, Ophiocimhium, Ampliipsila, 

 &c. may represent a most archetypal group of the Ophiacanthidce ^ 

 being very close to the Ophiomyxince on the one hand and to the 

 Amphilepididce on the other. Microphiura may be very embryonal, 

 having the oral papillae completely soldered together and the lateral 

 arm plates extremely well developed. In a very small and young 

 specimen, of which the genus is indeterminable, I have observed 

 that every essential structure is similar to that of Microphiura, 

 the oral papillœ being completely soldered together, the genital 

 slits invisible, the second oral tentacle pore opening entirely outside 

 the oral slits, the tentacle pores provided with a crescent-shaped 

 scale, and the lateral arm plates almost completely covering the 

 entire surface of the arm. I therefore consider Microphiura to be 

 probably a pa3domorphic form, granting that the spscimens described 

 by MoRTENSEN are sexuaUy mature ; it is in my opinion not truly 

 archetypal. 



I have already mentioned that the very good development of 

 the lateral arm plates, which separate the dorsal and ventral arm 

 plates from each other, is an embryonal feature. Following this 

 principle, the majority of the Ophiacanthidce are embryonal in the 



