A COLLECTION OF HYDROIDS. 301 



the oriu'iu of the hydrocauhi.s from the hydrorhiza, and the 

 bilateral character of the perisarc of the hydrotheca; two of 

 the teeth are lateral, one on the side facing the hydrorhiza, 

 and one on the opposite side. 



There is a four-flapped opei'culnni, forming- a four-sided 

 pyramid. 



The cavity of the hydrotheca is partially shut off from the 

 cavity of the hydrocaulus by a diaphragm (d.), which resembles 

 that seen in a Campanularian. The opening of the 

 diaphragm is excentric^ being nearer the side facing the 

 liydrorhiza. 



Length 0'40 nnu., greatest breadth 0"26 nnn. The thick- 

 ness of the perisarc varies considerably on the two sides ; on 

 the side facing the hydrorhiza it is 4/x and on the opposite 

 side 10^ (PI. XLVIl/fig. 22). 



Hydranth. — The polyp has the typical sertularian 

 structure. The hydrotheca is lined by a thin epithelium of 

 ectoderm (fig. 22, e.-'t.) which generally joins the ectoderm of 

 the hydranth near the diaphragm ; but it appears not to be 

 very constant in its place of junction. There is the usual 

 dilatation of the coelenteron (CD.) which is on the side facing 

 the hydrorhiza. The hypostomeis more or less hemispherical. 

 There is a single verticil of about twenty tentacles. The 

 nematocysts are few and small ; they measure about 3 fx in 

 length and 0'7 /i in width. 



The hypostome has a narrow endodermal epithelium ; the 

 outer side of the dilatation of the coelenteron is lined by a 

 comparatively flat undifferentiated endoderm {u.i-.). The rest 

 of the hydranth is lined by elongated vacuolated cells with 

 granular cells (gr.c.) wedged between. At the base there 

 are some clumps of special granular cells {gl.c). 



GoMOSOME. — Unknown. 



Systematic Positiox. — The present hydroid is undoubtedly 

 closely allied to Calamphora parvula^ Alhiian, and Ser- 

 tularella solitaria^ Nutting, In the former the hydro- 



^ Annum, J. G., ' Challenger Reports," voL xxxiii. p. 29. 



- Nutting, C. C, ' American Hydroids,' pt. ii " Sertularedse," p. 89. 



