AND SPECIES OE nTDROIDA. 278 



Gonosome. Not known. 



Locality. Japan, Capt. St. John. 



The liydropbyton in the present species is very opaque and 

 dark-coloured ; when boiled in a solution of caustic potash, it be- 

 comes much lighter and more transparent ; and it is only then 

 that a knowledge of the true form of the hydrothecae and of their 

 relation to the other parts of the Hydroid can be obtained. It 

 will be then seen that they are nearly cylindrical in form, with a 

 very definite floor, and closely adhere to the sides of a continuous 

 axile tube, with which the hydrotheca commimicates by a central 

 orifice in its floor. The hydrothecse are disposed so as to form 

 four longitudinal rows, which are approximated in pairs, so that 

 two rows run down one side of the stem and two down the other. 



The specimen was imperfect, and was in great part enveloped 

 by the adherent tubes of the two Campanularians described 

 above as C. grandis and C. gracilis. 



PEEiciiADiUM, gen. nov. 



Trophosome. Hydrothecse more or less immersed and closely 

 set round bifurcating ramuli, which spring from the sides of a 

 common stem. 



Gonosome. Gonangia scattered, springing from between the 

 hydrothecse. 



The genus PericZa(7iw«i approaches Thuiaria, from which, how- 

 ever, it difi'ers in the disposition of its hydrothecse. In Thuiaria 

 the hydrothecse are disposed distichally, being always arranged 

 in two opposite longitudinal series, while in Pericladium they sur- 

 round the ramulus on all sides. 



Pericladium bidentatum. Plate XX. figs. 1-4. 



TropJiosome. Stem attaining a height of about 4 inches, simple, 

 not fascicled ; hydrothecal ramuli cylindrical, two or three time? 

 bifurcate, attaining a length of about | of an inch, springing from 

 the main stem in a close spiral. Hydrothecse flask-shaped, im- 

 mersed for the greater part of their length and arranged in im- 

 bricated or closely approximate alternating verticils, but towards 

 the proximal end of the bifurcating ramulus separated from one 

 another and irregularly scattered ; orifice with an acute tooth on 

 each side. 



Gonosome. Gronangia carried on tlie upperside of the hydro- 

 thecal ramuli near their origin from the common stem, obovate, 



