MUSEUM OF COMPARATIVE ZOOLOGY. 135 



one fourth the distance between base and apex there is found what resembles 

 the broken base of a single branch. Stem non-fascicled, bearing alternate pinnse. 

 Hydrothecse deep, nearly cylindrical above, and tapering to the place of origin 

 of the mesial nematophore. The hydrotheca has a single mesial nematophore, 

 which is free, trumpet-shaped, and springs from a slight protuberance below 

 the base of the hydrotheca. Supracalycine nematophores free, moimted on 

 projections from the pinna, and overtopping the orifice of the hydrotheca. 

 Depth of the nematophores about one (quarter that of the hydrotheca. 



Gonosome : — There are three gonosomes. They resemble spikes of barley, 

 and arise directly from the stem by a short peduncle. The axis of the gono- 

 some is about the size of the main stem, near the place of origin of the gono- 

 some, and from it arise verticillate ribs. In each verticil there are three main 

 branches, each of which divides into four ribs by two divisions. These ribs 

 bear a line of nematophores along their upper side. There are no hydrothecae 

 on the ribs or at the base of the verticils. The gonangia are found in gono- 

 phores, which arise in the axils of the undivided verticils, from the axis of 

 the gonosome. They seem to be protected by the ribs of the gonosome in 

 somewhat the same manner that the gonophores in Cladocarpus are protected 

 by phylactogonia. 



The bottle which contains this specimen is without label. The gonosome of 

 C. gracilis resembles in its staghorn-Iike ribs the " brush " of Thuiaria thuja. 

 In other respects there is no likeness between these two hydroids. The " brush " 

 of T. thuja is the whole hydrocaulus modified, while the gonosome of C. gracilis 

 is a specialized branch. The gonosome of Callicarpa is homologous to the 

 corbula of an Aglaophenia. I do not regard the corbula of this and some other 

 genera as homologous to a pinna, and its ribs to modified mesial nematophores, 

 but as a metamorphosed branch. The spike of Callicarpa is a modified branch, 

 as its relationship to Hippurella shows. The discussion of the homology of the 

 corbula of another genus is given under the genus Pleurocarpa. 



Cladocarpus compressus, n. s. 



Trophosome : — Hydrocaulus attaining the height of eight inches. The 

 main stem consists of two sections, neither of which is fascicled. The lower 

 part is of light brown color, and has a smooth surface without nematophores. 

 It takes up about one third the whole length of the stem. The remaining 

 portion of the hydrocaulus, or the second part of the stem, is of smaller diame- 

 ter than the former, of light straw color, and bears a single row of denticulated 

 nematophores. It terminates in the immediate proximity of the lowest pair of 

 pinna;, where it becomes twisted three times. Still a third division of the stem 

 is that which carries the pinnse. It bears no medial row of denticular nemato- 

 phores, but in other respects resembles the second of the two divisions of the 

 hydrocaulus. Hydrocaulus unbranched, with alternately arranged pinnae. 

 Hydrothecae closely crowded together in the pinna. Margin toothed ; shape 

 cyathiform, with indentation on the face. Supracalycine nematophores not 



