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Show 188 MESSRS. L. MURBACH AND C. SHEARER ON [June 16, expect to find it in the other species when these are closely studied. The four species of Gonionemus at present known are as follows:- 1. Gonionemus vertens A. Agassiz (2). 2. „ murbachii Mayer (29). 3. ,, suavensis Agassiz &, Mayer (3). 4. „ agassizii, sp. nov. In general appearance and structure the four species differ as follows :- Gonionemus vertens has much the tallest bell and heaviest tentacles, longest digestive cavity, and oval large marginal papilla?.-Pacific. Gonionemus murbachii has the bell low, the velum well developed, the tentacles very flexible, the proboscis short.- Atlantic. Gonionemus suavensis differs from the other species in the presence of four green spots on the proximal ends of the radial canals, in the absence of subumbrellar papilla?, and the extent and position of the ovaries.-Pacific. Gonionemus agassizii has the bell lower than in G. vertens, yet taller than in either of the other two species. It has a larger number of tentacles (in fully grown specimens probably over a hundred), which are shorter and smaller than in the other species. The depression in the roof of the stomach is more marked in this species than in the others with the exception of G. suavensis.-- Pacific. Species incerta. (Plate XX. fig. 2.) The following description refers to a peculiar form, a single individual of which was collected by Prof. Kincaid at the St. Paul's Island, Pribyloff Islands. It is very badly preserved, and on this account no definite identification has been attempted. Bescription.-The bell is 18 m m . high by 10 m m . broad at its widest part, a little above the region of the velum. The general shape and proportions of the bell are represented in PI. X X . fig. 2. The bell is drawn in somewhat towards the mouth, and through this the smooth cylindrical proboscis extends a short distance. The proboscis bears four well-marked cylindrical mouth-lobes, one of these being much larger than the others and rolled up on itself, looking like a small contracted tentacle. Connecting the four radial canals and running in the bell-substance are delicate transverse lines represented in the figure. Some of these are larger than others, and look almost like small connecting canals. The radial canals are thick, and along their |