86 AMERICAN HYDROIDS. 



The stem of this species differs from that of nearly, if not all, other American Plnmularidre 

 in having the hydrocladia borne on a tube which is central and not anterior to the accessory tubes 

 of the fascicled structure. The accessory tubes are smaller than in most species, which may 

 account for Doctor Fewkes's error in describing the stem as not fascicled. 



Types. In the Museum of Comparative Zoology, Cambridge, Massachusetts. 



HALOPTERIS Allman. 

 Hatopleris ALLMAN, Mem. Mns. Cornn. Zool., V, No. 2, p. 32. 



Trophosome. Stem and hydrocladia divided into internodes, the hydrocladia pinnately 

 arranged. Hydrotheca' cup-shaped and furnished with a pair of lateral nematophores which are 

 fixed instead of free, as iu the other Eleutheroplea; mesial nematophores free. 



Gonoftome. ] Gonangia oval, sac-shaped, borue at the bases of the hydrotheca? and unprotected 

 by any form of phylactogonia. 



This genus is of peculiar interest from the fact that it combines the characters of the two 

 great groups of Plumularidse having the fixed nematophores of the Statoplea represented by the 

 lateral pair, and the free mesial nematophores of the Eleutheroplea represented by the mesial 

 and cauline nematophores, all of which are biihalamic. In most respects, however, it shows very 

 decided affinities with the latter group. Not infrequently the upper part of the hydrocladial 

 internode is separated from the rest by a distinct node, thus forming an intermediate internode 

 which is distinctly a character of the Eleutheroplea. The shape of the hydrothec.e, together with 

 the arrangement of the internodes, especially when the intermediate interuode is present, the 

 alternating oblique and straight nodes, and the shape and location of the gonangia, show that 

 this genus has decided affinities with the catharina group of the genus 1'lumuhiria. 



HALOPTERIS CARINATA Allman. 



(Plate XVII, figs. 7-9.) 

 Ilalopterifi carinaia ALLMAN, Mem. Mns. Com]). Zool., 1877, V, No. 2, p. 33. 



TrophoHomi'.-- Colony attaining a height of about 2 inches, sparsely branched; stem not 

 fascicled, divided regularly into interuodes, each of which bears a hydrocladium on a process 

 from near its proximal end; hydrocladia alternate, first internode short, the others long, each 

 bearing a hydrotheca; nodes oblique. Ilydrotheca' rather deep, cup shaped, each with an 

 anterior keel ending in a blunt marginal tooth, the margin being otherwise entire; upper third 

 of hydrotheca free from the internode; supracalycine nematophores borne on long curved lateral 

 processes from the interuode, cup-shaped and immovable; two mesial nematophores to each 

 internode, one above and one below the hydrotheca; cauline nematophores fixed. 



Gonosome. Gonangia oval, sac-shaped, borne at the bases of the hydrotheca', and not 

 protected by phylactogonia of any kind. 



Distribution. Off Carysfort fieef, 35 fathoms (PourtaH's). Between Eleuthera and Little 

 Cat Island, Bahamas, 3 to 13 fathoms, State University of Iowa, Bahama Expedition. 



As before remarked, there is an occasional intermediate hydrocladial iuteruode. Bale says 

 concerning this species: In Professor Allinan's figures, however, the cup of the sarcotheca is 

 shown raised above the margin of the hydrotheca, and the long tubular adnate portion seems 

 rather to resemble the peduncles, which in several species of Plumularia support the sarcothecit, 

 than an intimate part of the latter organs. 2 An examination of the specimens at hand fully 

 bears out Bale's supposition. 



These supports are doubtless homologous with the processes bearing the supracalycine 

 nematophores in riumularia catharina, for instance, and renders still more marked the resemblance 

 previously alluded to between IJaloptcrin and the cathnrtnn type of Pliniiiihiria, the main difference 

 being in the fact that in Halopteris these uematophores are entirely immovable. 



Type. In the Museum of Comparative Zoology, Cambridge, Massachusetts. 



1 Hitherto uutlescribed. ! The Geuera of the 1'luiiiulariidu;, pp. 7, 8. 



