OF THE ACALEPH^ OF NOKTH AMERICA. 311 



times a quadrangular form, — An acquaintance witli tlie morphology of the moulli of other Medusae necessary to under- 

 stand the generic characters of Staurophora, 306. — It has really a mouth, — I have seen it eating, 307. — Slaurophora 

 laciniala, the name of our species, — Organs of reproduction, — Color of tliis species, 308. — Slaurophora belongs to 

 the same family with TlimiimuUins and Tiaropsis, — Euilora and Berenice of Peron are also naked-eyed Medusa;, — 

 the family BercnicidcB of Peron an artificial group, 30!). 



EXPLANATION OF THE PLATES. 



Plate I. — IIippocrkne superciliaris. 



Figures of natural size and enlarged in different positions. Fig. 1, 2, 3, and 4, eidarged ; Fig. 5 to 11, of natural size, 

 slightly exaggerated. Compare page 257. 



Fig. 1. Enlarged, seen in profile, slightly overhanging, with the tentacles raised, while in Fig. 5 they are spreading 

 sideways and downwards. 



Fig. 2. Seen from below, the mouth in the centre, and the branching fringes around it ; the four sensitive bulbs, with 

 the eye-specks, beyond which the tentacles are extended ; the circular chymiferous tube and the nervous cord on its inner 

 margin ; the undulations produced by the inner muscles, and the inferior partition. 



Fig. 3. Seen from above, the central digestive cavity being empty, and the four radiating chymiferous tubes very prom- 

 inent. The chief difference between this figure and the preceding consists in the contracted state of the tentacles. 



Fig. 4. In the same position as Fig. 3, only the tentacles are still more contracted, the central digestive cavity dis- 

 tended, and bunches of eggs are hanging around it. 



Fig. 5. A specimen suspended motionless in the water, with its tentacles extended. 



Fig. 6. The same, seen from above. 



Fig. 7. Specimen contracted to the utmost, turned upside down, with its tentacles drawn in and the lower partition 

 turned inwards. 



Fig. 8. The same, seen in profile, somewhat turned sideways. 



Fig. 9. A specimen contracting to push forwards, the tentacles following behind. 



Fig. 10. A specimen in a similar state of contraction, moving sideways. 



Fig. II. A specimen at rest, as those in Fig. 1 and 5, but the tentacles drawn in. 



Plate II. 



This plate represents microscopic details of Hippocrene superciliaris. 



Fig. 1. A tentacle raised upwards, with a dark eye-speck, a, at its base ; i, an elongated portion of the tentacle ; c, its 

 middle in a more contracted state, and d, the tip. See page 270. 



Fig. 2. The tip of the tentacle much enlarged ; a, the larger inner cells ; b, the smaller outer cells. 



Fig. 3. A portion of the tentacle in an elongated state, much enlarged ; a, the large inner cells ; b and c, the smaller 

 external ones. 



Fig. 4. The tip of the tentacle, in a less elongated state than in Fig. 2 ; a, the large.inner cells ; b, the smaller external ones. 



Fig. 5 and 6. Superficial epithelium. In Fig. 5, which is taken from the upper surface of the disk, the cells are very 

 distinct and polygonal, some of them containing nuclei. In Fig. 6, which is taken from the lower margin, the cells are 

 irregular, and their nuclei still more so. 



Fig. 7. A part of the central digestive cavity, with the crosier-shaped radiating tube rising from one of its corners ; a, 

 the central cavity itself; b, the origin of the radiating tube ; c, the arch which it forms above the digestive cavity. See 

 page 264. 



Fig. 8. The lower extremity of the radiating tube branching into the circular tube ; a, the dilatation of the tube behind 

 the sensitive bulb, from which the two branches of the circular tube, i, b, arise ; c, the vertical part of the descending tube. 



Fig. 9. A portion of the vertical tube ; a indicating its cavity, and b its walls, which are equally distinct in Fig. 7 and 8. 



