'"l'«93!'] PROCEEDINGS OF THE NATIONAL MUSEUM. 161 



tion I have modified somewhat that giveu byHertwig, thereby extend- 

 ing the limits of the family so as to include certain forms with short, 

 stout, n on -retractile tentacles. I consider the presence of a strong 

 mesogltpal sphincter and the absence of acontia the two most marked 

 characteristics of the family, the number of mesenteries being of less 

 importance, for although the majority of forms to be assigned to the 

 family possess numerous perfect mesenteries there are nevertheless 

 some in which only the mesenteries of the first cycle are perfect. These 

 are, however, so (;losely related to those with numerous perfect mesen- 

 teries that it seems to me injudicious to separate them. 



Andres ('83) independently established a family I'aractidfe, which 

 probably is identical with that of Hertwig. The definition was, how- 

 ever, founded altogether on external characters, Avhich are undoubtedly 

 of less value in Actinian taxonomy than are anatomical features. 



Genus PARACTIS, M.-Edw. 



Paractidse with smooth body-surface, without papilhe or marginal 

 spherules; tentacles, slender, not excei)tionally numerous, nearly equal 

 in length and strength; margin not lobed. Sphincter widening some- 

 what abruptly in its upper part, and occupying near the margin nearly 

 the entire thickness of the mesogloea. This is the definition which Hert- 

 wig ('82) gives of the genus, with the exception that he includes in 

 the definition the presence of " numerous longitudinal furrows of the 

 wall,*' which it appears to me limits the genus too narrowly, and by what 

 is probably a more or less tiivial character. He himself points out the 

 possible alliance of his F. excavata to the Actinia peruviana of Lesson, 

 in which the longitudinal furrows, are wanting, except near the base, 

 the column wall being described as smooth. 



In the Albatross collection there are two forms which must be as- 

 signed to the genus as here limited, although they differ greatly in 

 certain respects. In one, the column wall, though not particularly 

 thick, is leathery, while in the other it is of a much softer consistency; 

 and again in one the radial muscles of the disc and longitudinal muscles 

 of the tentacles are imbedded in the mesoghea, Avhile in the other they 

 are ectodermal. Whether this latter feature is one sufficient for ge- 

 neric distinction can only be determined by the examination of a large 

 number of Paractida'. I propose to place both the forms provisionally 

 in the genus Paracfis, leaving it for future workers to decide as to the 

 advisability of their separation. There is one feature in which they 

 both agree, and that is in the sliai)e of the sphincter nuiscle, which from 

 being very narrow below gradually widens as it nears the margin, and 

 has consequently a somewhat club-shaped form. Apparently /*. exca- 

 vata has a similar sphincter, thcmgh Hertwig has given no figure from 

 which its form may be accurately determined. 

 Proc. N. M. 93 11 



