76 AMERICAN HYDROIDS. 



the branches which bear the hydrocladia being divided into long intornodes, each of which bears 

 a hydroeladium on its upper side aud distal end; a hydrocladium springs from the stem at each 

 forking; hydrocladia divided into alternating hydrothecate and intermediate internodes, which 

 are short and join each other under the hydrotheca' by oblique nodes and above the hydrothecre 

 by straight nodes. Hydrotheca-. large, campanulate, separated by at least twice their height; 

 supracalycine neinatophores present, reaching above the level of the hydrotheea? and borne on 

 distinct processes from the hydrocladial internodes; a mesial nematophore at the base of each 

 hydrotheea, and two to each intermediate interuode; cauliue nematophores numerous in linear 

 series along the upper side of each branch. 



(fonosome. Gonaugia sac-shaped, borne on short processes below the bases of the hydrotheea', 

 each being protected by a pair of basal nematophores. 



Distribution. Off Pacific lleef (Pourtales); />'//,T, off Barbados, 7(i fathoms; Albatross, 2fi 

 stations in the North Atlantic, from Marthas Vineyard southward, 12 to 290 fathoms; Charleston, 

 South Carolina (McCrady). 



In the northern part of its range this beautiful species grows to a much greater height than 

 the specimens described by Professor Allman under the name Monostcechas dichotoma, aud often 

 assumes a straggling habit of growth very different from the compact, flabellate form of the type 

 The mode of branching seems to be constant, and I have seen no deviation from it in the immense, 

 number of specimens from the Albatross collections which I have handled. Although I have been 

 unable to find specimens iutergradiug entirely between Allman's type and the straggling form just 

 mentioned, it hardly seems justifiable, in the absence of any good structural point of diffei'ence 

 to separate the two aud regard them as distinct. 



Specimens of Pliniiulitri/i qiKidridens from Charleston, which Doctor Agassi/ kindly sent me from 

 the Museum of Comparative /oology, agree very well with specimens of Mononta'chas dichotom t 

 Allmau, except in size, the Charleston specimens being much smaller than those secured by the 

 Jilake and the Albatroxx. Otherwise the two forms agree so exactly in detail that 1 am unable to 

 separate them, aud am therefore compelled to regard .17. dichotoma as a synonym of /'. ijuadridenx. 

 The genus Monostaschas, however, seems tenable, and necessitates the removal of the species to 

 that genus. 



ANTENNELLA Allman. 

 38. 



Anlmiiella ALLMAN, iloin. Mus. Couip. Zool., 1877, V, No. 2, p 



TropliosoiHt'. Colony consisting of hydrocladi 



i'. Colony consisting of hydrocladia springing directly from the hydrorhiza 

 without the intervention of stems or branches; hydrocladial interuodes and hydrothec;e as in the 

 catharina group of the genus Plumularia. 



Gonosome. Not known. 



Hincks regarded a species of this genus as a variety of Plumularia catliarina which had 

 adopted a different habit of growth. In one species, J'lii>iniln>-i<i Jilicaulis Poeppig, the mode 

 of growth of both Plumitlaria aud Antennella is seen in a single colony, but this may possibly 

 represent stages of growth rather than an essentially different habit. The entire absence of the 

 stem seems to be a constant character of the present species, however, and until iutergrading 

 forms an- found it is probably wisest to leave Allmau's arrangement undisturbed. The writer is 

 inclined to think, however, that the group of genera first described by Allman and arranged 

 almost, if not quite, exclusively on the branching habit of the various species is not entirely 

 satisfactory, throwing together as it does species quite dissimilar in details of structure and 

 separating into distinct genera forms which agree exactly in details, such as the arrangement 

 of interuodes and nematophores aud shape of the hydrotheea'. It seems unbelievable that this 

 identity of detail should be the result of approximation from different types rather than an 

 evidence of close relationship. It may ultimately prove best to gather into a separate genus 

 all of the species now iu the genera riiiuil<iri<i, Monoxta-t-ltas, aud Antennella, which have the 

 arrangement of internodes, hydrotheciv, and neinatophores, which is found in Plumularia 

 catJiariua, and consider the manner of branching as of secondary importance, useful merely for 

 specific characters. 



