TIAROPSIS. 



69 



TIAROPSIS Agass. 



Tiaropsis Agass. Mem. Am. Acad., IV. p. 289. 1849. 

 Tiaropsis Agass. Cont. Nat. Hist. U. S., IV. p. 355. 1862. 



Tiaropsis diademata Agass. 



Tiaropsis diademata Agass. Mem. Am. Acad., IV. p. 289, PI. 6. 



Tiaropsis diademata Agass. Cont. Nat. Hist. U. S., HI. p. 354, PL 31, Figs. 9-15; IV. pp. 308 



-311, Figs. 45-48. 1862. 

 Tiaropsis diademata A. Agass. Proc. Bost. Soe. Nat. Hist., IX. p. 93, Fig. 10. 

 Tiaropsis diademata MoKCH. ; in Beskriv. af Groenland. 1857. 



This Medusa is one of the earliest visitants of our wharves in the 

 spring. In company with Sarsia and Syndictyon, it occurs in great 

 numbers during the spring months ; it attains its full size in a com- 

 paratively short period (Fig. 91), spawns during April and May, and 

 after that it is found but rarely, disappearing totally during the sum- 

 mer. Although so common, the Hydroid of this Medusa has not been 

 observed. Young MedusaB (Fig. 92), which are fully described in Pro- 



fessor Agassiz's Contributions, are exceedingly numerous. The tentacles 

 develop independently of the eyes, while the latter never increase in 

 number. (See Fig. 93.) For a more detailed description of their mode 

 of growth, see also my paper on the marginal tentacles of Hydroids. 



The Thaumantias Pattersonii of Greene seems to me, as far as I can 

 make out from his description and figures, to belong to the genus Tia- 

 ropsis. There must be some error in his view from above, in which he 

 represents black ocelli at the base of the chymiferous tubes ; I doubt if 



Fig. 91. Tiaropsis diademata, natural size. 



Fig. 92. Young Tiaropsis, having twenty-four tentacles. 



Pig. 93. Young Tiaropsis, having foi-ty tentacles, c, eye-speck ; /, digestive cavity ; g, chy- 

 miferous tube ; e, primary tentacles ; a, middle tentacle ; 6, third set of tentacles in pairs ; a, fourth 

 and fifth sets of pairs of tentacles. 



