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PROCEEDINGS OF THE 



[April, 1857. 



Remark. — This group is a large one, and contains so great a 

 variety of forms that it must eventually, it seems to me, be sub- 

 divided. Thaumantias plana Sars, T. lucida Forbes, Eucope 

 racliata Gegenb.. and Obelia commis surahs described below, are 

 quite distinct from the remaining forms. 



* Lateral cirrhi to the bulbs of the tentacula. 



EUCHEILOTA, nov. gen. 



The general form is hemispherical or bowl-like, the cavity of 

 the bell rather deep, so that the disk is only of medium thickness, 

 The digestive trunk is cylindrical and four-lipped as in Eucope, 

 with a small quadrate base upon the junction of the four radiate 

 tubes. The sexual organs are elongate, fusiform or oval, and often 

 contain a large sinus of the radiate tube. They are situate about 

 midway between the digestive trunk and the marginal canal. The 

 bell margin is highly complicated. The marginal capsules are 

 eight in number, two between every two radiate tubes. They are 

 rather large and contain a plurality of corpuscles, probably always 

 more than four. Corresponding to each is an easily discerned 

 ganglion-like enlargement of the marginal cord. The tentacula are 

 sixteen in number. They have large bulbs and slender lashes, 

 bearing rings of thread-cells, and one is found at the extremity of 

 each radiate tube, three more being found between every two 

 tubes. On each side, in the angle formed by the junction of the 

 bulb and margin, is found one of the small lateral tentacula. These 

 are delicate, transparent, and composed of a shaft formed of a pile 

 of cylindrical cells surrounded by a membranous sheath of great 

 tenuity. The extremity has somewhat the appearance of a thread 

 twisted in such a manner as to prevent its track being traced. I 

 have not been able to make out to my satisfaction the nature of 

 this part, but it is probable that the more easily discernible, some- 

 what disconnected masses of which it seems to be composed, are 

 the contents of thread-cells; the matrix in which these latter are 

 imbedded being of extreme transparency, and surrounded by a 

 membrane so delicate as to be difficult of definition. I think these 

 lateral tentacula are homologous with the small, transparent tenta- 

 cula described and figured by Gegenbaur in Thaumantias. (See 

 Gegenb. loc. cit. p. 239 pi. 8 fig. 3) Between every two of the sixteen 

 great tentacula thus described, there are a few marginal tubercles, 

 or knobs, bearing at their free extremities a few thread-cells. Each 



