^TsqT'] proceedings of the national museum. 1G5 



wall is ill some specimens thiiiiieitluiu it is lartlier down. The presence 

 of a pad may be due to contraction. 



The sphincter muscle, as Hertwig' i»ointe<l out, extends from the up- 

 per to the lower end of the wall. Its shape may be of generic impor- 

 tance, since it does not present the sudden widening near the margin 

 which is to be seen in the forms I have referred to the genus Paractis, 

 but tapers off very gradually indeed as it passes down the column. 



The specimens I examined did uot possess reproductive organs, so 

 that I can not decide the question Hertwig has raised regarding the 

 hermaphroditism of this form. 



Geuus Actinernus, Yerrill. 



Paractidte with thick column wall; margin lobed; tentacles short, 

 situated near the margin, the mesoghea thickened toward their bases, 

 so as to give them a im^re or less bulbous appearance. Sphincter 

 muscle rather weak (sometimes absent?). 



The genus Actinerrms was established by Verrill ('79) for a deep-sea 

 form obtained off the more northern portion of the east coast of the 

 United States, Verrill's definition and description speak of the mafgiii 

 below the tentacles being "divided into acute lobes or teeth continuous 

 with the body wall,'' the tentacles being aduate to these teetli. This is 

 the appearance which Actinernus nohiUs presents, but I have preferred 

 to speak of the teeth as thickenings of the inesoghea of the bases of the 

 tentacles, since this more nearly describes what obtains in A.2)lebeiHs, 

 and probably also in A. saglnatus. The sphincter nniscle is quite weak 

 in A. pJeheiufij as will be seen from the following description, and ap- 

 parently is wanting in ^4. ^<oi»i7i6', being indistinguishable with a pow- 

 erful lens. This character offers a marked difference, independent of 

 the nature of the tentacles between this genus and Antlioloha. 



The similarity which the figure of Polt/,si2)h()nia tuhcrom given by 

 Hertwig ('82) shows to an Actinernus is very striking and suggests 

 its possible reference to the latter genus. The lobed margin, the ba- 

 sally swollen tentacles, the disc marked with radiating grooves, the 

 chalice-like shape of the column, are all similarities which attract at- 

 tention. The sphincter muscle, too, though differing in shape from 

 that of ui. pU'beius, to be described below, is nevertheless mesodermal 

 and by no means powerful. The princi])al characteristic upon which 

 Hertwig relies in the establishment of the genus is found in the rather 

 large openings at the tips of the tentacles. Such openings are known 

 to be of frequent occurrence, and their enlargement within certain limits, 

 unaccompanied by a marked abbreviation or other alteration of the 

 tentacles, can not be considered sufHciently distinctive for the forma- 

 tion of a new genus. It seems to me that a reference of Polysiphonia 

 tuherosa to Verrill's genus Actinernus will place it with forms to which 

 it is far more closely related than it is to Polystomidimn. (See Appen- 

 dix, p. 209.) 



