254 PBOr. ALLMAN 0?r NEW GENEEA 



of the unfascicled portion, at once distinguish it from that species. 

 It is this fascicled condition which gives it the rigid habit which 

 has suggested its specific name. 



Such hydranths as are present in the specimen are evidently 

 those of a second crop which had replaced an earlier one — a phe- 

 nomenon not uncommon in Hydroid trophosomes. Each is borne 

 on the summit of an attenuated continuation of the original 

 branch ; and the new growths have much the appearance of having 

 been produced in the confinement of an aquarium ; at all events, 

 the attenuated extension of the branches is plainly not the normal 

 condition of these parts. 



HYBBACTINIIBM. 



Htdeactinia. 



Hydractinia monocarpa. Plate X. figs. 1-3. 



Trophosome. Basal expansion thin, furnished with well-de- 

 veloped chitinous spines ; spines with a continuous axile cavity, 

 and destitute of longitudinal furrows, except close to the base, 

 frequently bifurcate. Hydranths with about twelve tentacles. 



Gonosome. Blastostyles short, destitute of capitulum, and ter- 

 minating distally in a blunt point ; each blastostyle (female) car- 

 rying near its middle a single very large sessile spherical sporosac. 



Locality. Spitzbergen, Zool. Mus. Cop. 



This is a very interesting and well-marked form. It is easily 

 distinguished from S. echinata by its nearly smooth spines, and 

 especially by its noncapitate blastostyles, each with its single 

 sporosac. The sporosac is very large, and encloses a great number 

 of ova ; while that portion of the blastostyle which lies at the 

 distal side of the point of attachment of the sporosac is much 

 attenuated, and bent to one side by the enormously developed 

 sporosac. The blastostyle, with its sporosac, presents entirely 

 the condition met with in certain calyptoblastic Hydroids, in 

 which the gonangium contains only a single sporosac, by the 

 great development of which the blastostyle becomes more or less 

 atrophied and displaced. 



The basal expansion is thin, and its chitinous framework far 

 less developed than in H. echinata. The superficial coenosarcal 

 layer is very distinct, and is extended over the whole surface of 

 the spines. 



The chitinous walls of the hollow spines, besides presenting a 



