HYDROZOA RITCHIE. 835 



process which arises from the peripheral tube, and which tapers- 

 to the tip, where its diameter is considerably less than that of 

 the free portion of the sarcotheca. Often the sarcotheca is 

 represented only by the stiff basal portion, for the distal portion 

 is delicate and is slightly attached. Gonosome. — Not present. 



Remarks. — I have compared this specimen with fragments of 

 the specimens collected by the " Challenger " and named by 

 Allman Perisiphoina Jilicula and Perisiphonia pectinata.*^. 

 There can be no doubt it is specifically identical with the 

 former, notwithstanding discrepancies between the characters 

 given above and Allman's description and figures. Comparison 

 of a fragment of one of the specimens of P.fiUcida examined by 

 Allman with his description shows that the latter is misleading. 

 Thus, the hydrothecse are described as "flask-shaped," with the 

 "neck " short and stout, and in the figures they are represented 

 as retort-shaped with a bulging proximal portion tapering 

 upwards into a much narrower so-called " neck." In reality, the 

 diameter of a hydrotheca is almost constant throughout, and the 

 neck can be distinguished only because of its outward curvature. 

 The distinction between a hydrotheca and its " peduncle " is 

 exaggerated in the figures, for in the specimen their continuity 

 of profile is unbroken, and only the internal diaphiagm marks 

 their junction. The sarcothecse are misrepresented in Allman's 

 fig. 2, for all the perfect specimens I have seen consist of a 

 fixed process from a stem tube, surmounted by a short movable 

 cylindrical limb. Again, in Allman's figures, a sarcotheca 

 springs from the axial tube immediately beneath each hydro- 

 theca, but I find no tiace of such a sarcotheca. These modifica- 

 tions show that no difference of import exists between Allman's 

 P. Jilicula and the "Thetis" specimen — that their dimensions 

 are also in close correspondence a glance at the following table 

 will show. 



Regarding the identity of P. Jilicula, Allman, and P. pectinaia,. 

 Allman, which Pictet and Bedot have urged, there is more room 

 for doubt. The fragment of the type specimen of P. pectinata^'^ 

 which I have examined differs from P. Jilicula in res])ect of the 

 greater distance which separates the hydrothecse ; the greater 

 length and slenderness of their free portions ; the sharp angle at 

 which they bend away from the stem, and which is indicated on 

 the abcauline wall by an internal thickening of chitin ; the 

 greater length of the sarcothecse, which project sometimes to the 

 height of the hydrothecse, and which are less distinctly, or not at 



91 Allman— Rep. Sci. Ees. "Challenger," Zool., xxiii., 1888, Hydroida, 

 p. 45, pi. xxi., figs. 2, 2a, 2&. 

 "' See Plate Ixxxvii., fig. 2. 



