36 AMERICAN HYDROIDS. 



As an outcome, of this we have, many structures that are exquisitely beautiful or graceful, or 

 at times merely grotesque. 



In a few cases the rugosities are longitudinal, rather than transverse or annular, and we have 

 the ribbed gonangia, .such as are seen in <SV rfnl<ii'< Ilii < j>!xr<>j>iit< (Plate XXVI, tig. 7), Ablet inaria 

 graciliK (Plate XXXV, tig. 1), and Abn-fliKirl/i <-<>xtn1<t (tig. 104). In a number of species the 

 superficial ornamentation takes the form of horn-like processes or long spines, which may be two 

 in number and borne on the shoulders of the gonangium, as in Thuiaria argentea (Plate XII, 

 tig. 9) or T. rnbuxta (Plate VII, tig. 7), or there may be four or more radiating from the 

 gonangial aperture, as in X ffnliin //</ quadrata (fig. ~L29). In the male gonangia of several 

 species of Dlplias'ni there are a number of conical spines arranged in a circle around the distal 

 end, as in I), paarmanni (&g. 130), or the whole of the distal end of the gonangium may be 

 bristling with spines, as in X rfadaretta Inri/ii/n (Plate XXII, tig. 2). The extreme of spinulation 

 is reached in Ku'tnlni-!<i ,<-/i!i,,i<;irj><t Allman (tig. 132) and DqiJiuxin illi/ita!!* (tig. 133), where 

 the entire surf ace of the gonangium is beset with spines. A very curious ornamentation is found 

 in Selaginopsis ornata (tig. 134). where there arise from the distal surface eight long slender bifur- 

 cating processes which may be for the purpose of forming a sort of pseudo-marsupium as a 

 protection for the ova in the later stages of their development. 



Still another kind of gonangial ornamentation has already been discussed, that is the broad 

 leaves, four or eight in number, that form the marsupial chamber in the female gonangium of 

 several species of ]>ij>li<ix!a (tig's. 91-97). 



A very graceful surface marking is seen in Syntheovwm. catnpylocarpum, where the gonangia 

 are furnished with two series of opposite, and gracefully curving rugosities forming a bilateral 

 ornamentation that is very rare among the Hydroida (tig. 135). 



The gonangial aperture is usually either round or squarish in outline, and is always ter- 

 minal in this group, never taking on the lunate form and lateral position seen in some of the 

 Plumularidse. 1 As would be expected, the aperture of the female gonangium is, in general, 

 considerably larger than that of the male. Probably the largest aperture in proportion to the 

 size of the gonangium that I have seen is that of Si /fnlnrrllii niii/nxfuina (Plate XX, fig. 9). In 

 many eases the aperture is elevated on a sort of collar which may be a simple narrow band, as 

 in SertulaTia gracii/is (Plate III, tig. IH), or a broad band, as in Abietwiaria <<><! (tig. 120), where 

 it is quite conspicuous on the upper surface of a top-shaped gonangium. Often this collar is 

 produced into a tube with a flaring or trumpet-shaped distal end, as in Sertvlarella filiformis 

 (tig. 11:'.), and S. /iii-riiliiiinilin (Plate XXIII, tig. 8). In some eases there appears to beatulie 

 within a collar, as in Sertitlaretta tricuspidata (Plate XXV. tig. 5). Rarely this collar is quadrate 

 in form, as in Sertula/rella fvgiformis (Plate XX, tig. 4). In many cases, however, the mouth is 

 not elevated above the general surface of the top of the gonangium, where it may be surrounded 

 by a series of from two to tive blunt spine-like prominences that are often used as specific char- 

 acters, as, for example, in SertulareUa polysonias (&g. 12f>), .V. <-<>i, fmin (tig. 1 24-), and S. cij>/,.n/ 

 (Plate XXI, tigs. 7 and !). This kind of ornamentation appears to be confined to X rfiilii/'' l/<i. 



Superficial color markings are exceedingly rare on the gonangia. The only cases that I know 

 of among American Sertulariche are found in Abii'tiiinrlii t-axtiiiti (Plate XXXVI, tig. 12), where 

 the summits of the longitudinal ridges are marked by distinct black lines that are very conspicu- 

 ous in comparatively fresh specimens, and the same thing is much less conspicuously seen in 

 J. tuiij'lioni (Plate XXXIV, tig. 4). 



The gonangia of several species of Thuiai'nt, as T. ilmntriniil,* (Plate VIII, fig. 6), and 

 Abietinaria, as in A. mrliibiHx (Plate XXXII, tig. 7), are peculiar in having a number of sharp 

 chitinous teeth arranged in a circle on the inside, just below the aperture. I am unable to under- 

 stand the function of these teeth, unless they serve as a sort of anchorage for the deckenplatte, 

 very much as similar teeth at the bottom of the hydrotheca- of certain campanularians are. sup- 

 posed to serve for points of attachment for the hydranth. 



The text figures 99 to 139 are all drawn to the same, scale, and show the variation in si/c that 

 is found among the gonangia of the Sertularida'. 



'See Part I, pi. ix, fig. 3. 



