308 HYDROID^. Part IV. 



development as the genera distinguished above among the Tubularida?, and one 

 of these medusae, that of Clytia cylindrica, resembles so closely the genus Tia- 

 ropsis, that I have, for many months, supposed it to be the young Tiaropsis, until 

 this was, also, finally obtained. There can be no doubt now that the naked-eyed 

 medusae, with free eyes between their tentacles, arise from the creeping Campanu- 

 larians, referred by Lamouroux to the genus Clytia, and by Johnston to the genus 

 Campanularia projier. We shall see in the sequel that the branching Campanula- 

 rians, now mostly referred to the genus Laomedea, bear medusae with similar eyes, 

 but attached to the base of the tentacles, and that the type of Campanularia 

 dumosa, which belongs to the genus Lafoea of Lamouroux, produces Medusai Avithout 

 eyes at all, one of which has been described as Atractylis repens by Mr. Wright. 

 My son has lately traced the development of a species of Hydroids from our coast, 

 which I have identified with Lafoea cornuta Lamrx., the type of the genus, originally 

 found in Newfoundland. This establishes, beyond a doubt, the fact that there are 

 several families among the Hydroids thus far referred to the genus Campanularia. 



SECTION IV. 



TIAROPSIS DIADEMATA. 



This medusa is already minutely described in my first paper on the Acalephs 

 of Massachusetts ; I will, therefore, limit myself here to adding a few observations 

 upon the structure of the eyes and repi'oductive organs, which are not satisfactorily 

 represented in that paper. The form of the black pigment spot (PI. XXXI. Fi(js. 

 12, 13, 14, and 15, e) which is at the base of the pedunculated eye, is only 

 recognizable when viewed from above, in a line parallel to the axis of the disk 

 {Fig. 13, e), and then its broad conical outline is apparent ; and then only may 

 we see that it occupies the centre of a thickening of the inner wall [b), of the 

 edge of the disk, which, with the outer wall {a}), forms a broad, rounded prominence 

 above the eye peduncle. The ocular apparatus proper {Figs. 12-15, a^) hangs 

 from the under side of the disk and just within its edge. When seen from 

 above {Fig. 12) or below {Fig. 14), it has the form of a battle-door without a 

 handle, and in an end view {Fig. 15) it is transversely oval ; in fact, it is a thick, 

 transversely oval body, attached to the disk by a short and bi-oad pedicel. The 

 outer wall {Fig. 12, a^) is in direct continuation Avith the outer wall («) of the 

 disk ; it consists of a single layer of large, hyaline, broad, sharply polygonal cells, 

 which appear like a net-work covering {Figs. 13, 14, and 15). These cells are 



