420 PROVISIONAL SPECIES. 



Tuhularia mesembrijantliemum has the simple habit of T. indivisa, but with more slender 

 stems. It is a very beautiful species, with large delicately coloured hydranths. The processes 

 which crown the female sporosacs (Woodcut, fig. 84, b, c) arc laterally compressed, and possess 

 the form which Agassiz regards as characteristic of his genus Faryplia. They surround a 

 well-marked orifice in the summit of the sporosac, and the spadix may usually be seen protruding 

 through this in the mature sporosac, a condition which it appears is also common in the 

 American species which Agassiz would refer to Parypha. 



The male sporosac (d), instead of possessing the eight flattened processes of the female, has 

 four small round tubercles, bearing a close resemblance to the apical processes of Tubidaria larynx, 

 &c. There is here, also, a well-marked orifice, through which, as in the female, the summit of 

 the spadix may often be seen to be protruded. 



A remarkable fact noticed in the present species is the tendency of the spadix in the female 

 gonopbore to throw out from its base lobes which contain a continuation of its cavity, and which 

 not unfrequently become so elongated as to assume the appearance of radiating canals (c, a, a). 

 They were observed to vary in number from one to three, but were not invariably present. I 

 never met with them in the male. 



When a transverse section (f) of the stem is carefully made, its cavity is found to consist of 

 two great longitudinal chambers separated from one another by a partition formed by two plate-like 

 processes of the endoderm, which project from two diametrically opposite longitudinal lines until 

 they meet in the axis. The walls of these chambers are clothed with vibratile cilia, so minute as 

 to be with difficulty detected, and in this respect contrasting strongly with the long conspicuous 

 cilia which clothe the canals in the stem of Tubidaria indivisa. 



In making sections of the living stem, distinct evidence was afforded of the irritability of the 

 endoderm, which might often be seen immediately after the act of section to encroach upon the 

 cavity of the stem at the inner edge of the surface of section to such an extent as nearly to shut it 

 in. After a time, however, this encroachment of the endoderm recedes and fully exposes the 

 double cavity of the stem. 



Tubidaria mesembryanthemuni was obtained in consideraljle abundance in the more sheltered 

 parts of the Gulf of Spezia, where it occurred growing upon rocks at a little distance below the 

 lowest tide level. 



PROVISIONAL SPECIES. 



TuBULARiA ASPEUA, Allman. 



Under the provisional name of Tubidaria aspera, I would indicate a hydroid whose dried 

 stems are among the collection in the Jardin des Plantes. The soft parts have entirely dis- 

 appeared, so that nothing can be seen either of the hydranths or of the gonosome, and a satis- 

 factory determination is accordingly impossible. 



The stems form dense tufts, contorted and entangled below, and then, becoming free, attain 

 a height of about three inches, and a thickness of about -^th of an inch. They are mostly 



