MONOCrRArH OF JAPANKSE OPHIUEOIDEA. 63 



simple and not very stout. Ludwig's ' ilrst ventral arm plate ' is 

 present at the upper outer corner of the oral slit. The oral plates 

 are very slender and rather long. The interradial attachments of 

 the floor of the gastral cavity extend from the middle of the peri- 

 stomial plates outwards, and the radial attachments from the outer 

 end of the first vertebra3 outwards. The perihaemal canal and 

 genital bursa) communicate with each other, so as to form a single 

 cavity, which is however divided into ten radiating compartments 

 by the radial and interradial attachments of the floor of the 

 gastral cavity. The peritoneal cavity is perfectly divided into five 

 radial compartments, which is entirely filled up by the generative 

 glands. The ventral arm plates are present, being represented by 

 two or three secondary plates. The minute hooks of the arm 

 annulations are comparatively coarse, being composed of from one 

 to three supplementary booklets, besides the main terminal one. 

 In Astci'oporpa hadracantha, the radial shields are entire instead of 

 being composed of several secondary plates, stout and very thick. 

 The interradial attachments of the floor of the gastral cavity ex- 

 tend from the outer end of the peristomial plates outwards. The 

 ventral arm plates are entire, quadrangular, slightly separated by 

 the adradial parts of the b^ir-like lateral plates. The minute hooks 

 are much finer than those of the foregoing species, having only a 

 single supplementary booklet besides the main one, as in many 

 higher genera. The other structures are almost similar to those of 

 the preceding species. Tn higher genera with the arms branched 

 many times, the genital plates lie at the lower lateral sides of the 

 basal vertebrcT, and do not extend inwards to the first vertebra?, 

 as they do in the simple- armed genera. 



The species of Gorgonocephalus may be divided into three 

 groups on the ])asis of the attachments of the gastral pouches to 



