BORRADAILE— ON THE PONTONIIN^ 331 



Like other prawns, the Pontoniinse have an armature of spines on prominent 

 parts of the body. The use of this armature is realised at once when a prawn is 

 held alive in the hand. With its abdomen bent under the thorax, the animal is a 

 wedge-shaped object with the broad end in the direction of escape — that is back- 

 wards — and all its spines projecting forwards, so that they preserve for it any ground 

 which it gains in its struggles. The armature includes the rostrum and its teeth, 

 spines on . the carapace, on the two pairs of antennae, and often on the uropods, and 

 in a few cases a hooked projection at the back of the third abdominal segment. As 

 might be expected, it is less developed in the heavily built sedentary forms than in the 

 lighter species which live a more exposed life. 



The rostrum is probably seen in its earliest form in some of the species of Peri- 

 climenes. Typically, in this genus it is a straight, compressed, lanceolate structure 

 (Plate 54, fig. 10 a), of about the same length as the region of the carapace behind it, and 

 bears above and below a fairly deep, toothed crest, the upper crest being continued upon the 

 carapace by a row of two or three teeth. This form of rostrum is well seen in P. scriptus. 

 In certain cases it loses some or all the teeth of the ventral crest (Plate 54, fig. 9 a) or 

 even the crest itself Sometimes, as in P. hrevinaris, it becomes shorter. In other 

 species, as in P. ensifrons, it is curved upward at the end, so that the upper edge becomes 

 concave. Often, as in P. spiniferus (Plate 52, fig. 1 a), the curved rostrum is longer and 

 slenderer than the lanceolate type, and this tendency reaches its height in P. horradailei 

 and P. holumaduluensis. Urocaridella (Plate 53, fig. 2 a) has a very long and much 

 upcurved rostrum, toothed above and below, with the dorsal crest high at the base. 

 Urocaris loses the ventral teeth of this rostrum, and in some species has the organ 

 shortened by the loss of the slender distal part. Palwmonella has a shallow rostrum, 

 usually rather short and nearly straight. In Ancyclocaris it is short and straight, but 

 of a good depth. The more sedentary genera show varying degrees of reduction and 

 modification of this rostrum. The reduction is least marked in Harpiliopsis, Harpilius, 

 and Coralliocaris. In Harpiliopsis and Harpilius the rostrum hardly differs from that 

 of Periclimenes, but is rather small, and wide at the base. In Coralliocaris it is wide 

 and shallow and the teeth show signs of reduction, though they are usually present, at 

 least on the upper side. The free end is pointed both in dorsal and in side view, and 

 is not curved downwards. In Anchistus, Pontonia (Plate 57, fig. 29), and Conchodytes, 

 on the other hand, the rostrum, though it is more or less depressed at the base, is 

 (except in some species of Pontonia) deep and strongly compressed in the distal part. 

 The tip is bent downwards, and in side view rounded or diminished abruptly to a point. 

 Teeth are generally absent, but in some species of Anchistus there are small dentations 

 near the tip. In Typton the rostrum is peculiar, being small, compressed, almost or 

 quite toothless, and bent upwards at the free end, which is pointed. Stegopontonia and 

 Pontoniopsis (Plate 57, fig. 27), Pontonides (Plate 57, fig. 28), and some species of 

 Pontonia, difi'er from all other Pontoniinae in having a broad and very shallow rostrum, 

 lanceolate or triangular as seen from above. 



Of the spines of the carapace the most persistent is the antennal, which is never 

 entirely lost, though in some species of Conchodytes it becomes very blunt. The 



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