332 PERCY SLADEN TRUST EXPEDITION 



hepatic spine is generally present in free-living species but it may be absent even 

 here. It is found in Harpiliopsis but not in most species of Harpilius and Coralliocaris, 

 or in the still more sedentary genera. The supraorbital spine is kept only by some 

 Periclimenes (Plate 52, fig. l), Coralliocaris rhodope, Typton and Coutierea. In the 

 latter two cases it is very large. True branchiostegal spines are never found. There is 

 a pterygostomian spine in Coutierea. The lov^^er angle of the orbit may be produced, 

 but is generally blunt. 



Here may be mentioned the grooves of the carapace. These are not well marked 

 but very persistent. Groove h of Boas* is always present and there is usually some 

 trace of e, though the latter never crosses the back. 



The telson corresponds in width with the stoutness of the body, but always 

 narrows towards its hinder end, which is triangular, with sometimes, in primitive forms, 

 a pointed projection in the middle (Plate 52, fig. 1 p). On the dorsum of the telson are 

 two pairs of stout moveable spines. On each side of its hinder end are three spines, 

 of which the outer is short and stout, and the intermediate long and strong. The 

 sub-median is usually shorter than the intermediate and longer than the outer. It is 

 also more slender, and in primitive forms often feathered (Plate 53, fig. 2 p), showing thus 

 a transition to the feathered bristles of other Palsemonidse. In Conchodytes, Pontonia, 

 and some Anchistus, however, the sub-median and intermediate spines are nearly equal, 

 and in such cases they are usually of a clumsy, degenerate shape. The end of the 

 telson also often bears two or three pairs of fine, unfeathered bristles, whose presence 

 bears no relation to the degree of degeneracy of the species. 



The eyes are set widely apart on a region immediately below the rostrum. 

 Between them is a low swelling on which is seen the remains of the larval median 

 eye (Plate 52, fig. 1 c). Each eye-stalk starts with a narrow flexible region and suddenly 

 expands into a wide region with stouter walls. This region is usually a little flattened, 

 and at its end bears the cornea, which generally swells out beyond it at the sides. 

 Such an eye is well seen in Periclimenes (Plate 52, fig. 1 b) and the other little-modified 

 genera, and also in Harpiliopsis, Harpilius, and Coralliocaris. In Anchistus, Pontonia, 

 and Conchodytes, however, the eye, as might be expected, is smaller. It is also here 

 more cylindrical, and the cornea is either of equal width with the stalk or even 

 narrower. The eye of Pontonides (Plate 57, fig. 28 6), in spite of the general resemblance 

 of this prawn to Pontonia, is well developed and of the Periclimenes type. In Ancyclo- 

 caris, on the other hand, though the build of the body is Haipilius -like, the eye 

 resembles that of Poihtonia. Several interesting peculiarities are found. In Pericli- 

 menmus (Plate 55, fig. 20 a) the moderately large cornea has a curious cup-shaped depression 

 on the outer and lower side. In Pontoniopsis (Plate 57, fig- 27 h) the eye is large and 

 sub-globular, the cornea occupying one-half of the sphere. In the sub-genus Corniger, 

 of Periclimenes, the cornea is ogival, and in P. (C.) ceratophthalvius (Plate 54, fig. 9 h) this 

 peculiarity culminates in the appearance of a papilla, such as is found in Phyl- 

 lognathia and in the amphibious Ocypode ceratophthalmus. It would be interesting 

 to determine the physiological result of the structure which thus recurs in genera 

 * K. Danske Vidensk. Selsk. Skrifter (6), ii. ii. p. 25 (1880). 



