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median tubercle, which, as in A. bidens (Ohv.), is situated immediately behind the base 

 of the orbits: sometimes, however, the rostral crest reaches only as far as the origin of the 

 two oblique, lateral carinae, between which the carapace appears then flat and even. From 

 the small tubercle a low, obtuse, median carina runs backward to the middle of the carapace, 

 more conspicuously in young specimens than in the adult. Just midway between the median 

 tubercle and the anterior margin of the carapace, at either side of the rostral carina, a thin 

 lamellar crest runs obliquely backward from the rostral carina to the level of the median 

 tubercle; these two crests, the upper edge of which is rather sharp and that are marked with 

 2 or 3 violet spots, are bounding, posteriorly and from the inner side, the rather deep grooves 

 or depressions which separate the orbits from the rostral carina. The two crests or ribs from 

 which the specific name is derived, make an angle of nearly 45° with the rostral carina. The 

 orbital hoods that are rather much prominent, terminate anteriorly in an obtuse tubercle, 

 about as in A. bidens \ just near that tubercle and separated from it by a notch or emargination 

 the frontal margin carries, at either side of the rostrum, a slender spine like in A. cristatus 

 (vide: Coutiere, Les Alpheidae, 1899, p. 89, fig. 56); these spines measure one-third the length 

 of the rostrum. Between the rostrum and either spine the frontal margin runs S-like and is 

 fringed with long setae that reach to the end of i^' antennular article. Orbito-antennal groove deep. 



According to Coutiere (Les Alpheidae, 1899, p. 79 and p. 336) a pterygostomian spine 

 should not occur in the genus A/pkcus. A. bicostatus appears now quite remarkable by the 

 existence of a well-developed, acute, though small, pterygostomian spine. 



- Second article of the stout antennular peduncle as long as the visible part of the i^', 

 sometimes slightly shorter, sometimes slightly longer, 3''<^ article two-thirds of the 2°'^; anterior 

 margin of the articles with long setae, anterior margin of i*' article not bearing the spines 

 which in A. bidens are found here. Stylocerite terminating in a slender spine, that just reaches 

 beyond the i^' antennular article. Basicerite with a small, infero-lateral spine, that reaches 

 almost to the tip of i^' antennular article; carpocerite stout, distinctly shorter than the antennular 

 peduncle, reaching to the 2"'i third or to the middle of the 3"^ article. Like the antennal and 

 antennular peduncles, the scaphocerite also resembles that of A. bidens -, the lateral spine, in 

 which the concave, outer margin terminates and which is slightly curved inward, reaches 

 distinctly beyond the tip of the antennular peduncle, while the blade, fringed with hairs, is 

 just as long as that peduncle. 



Merus of the large cheliped of the male rather stout, its outer face twice as long as broad ; 

 both the upper and the inner margin end in an acute tooth, but they are for the rest entire 

 and unarmed. The large chela of the male, which much resembles that of A. bidens, is half 

 as long as the body and turned outward, the dactj-lus being placed at the outer side ; viewed 

 at from above, the chela appears little more than 3-times as long as the upper (inner) face 

 of the palm is broad. This chela is perfectly smooth, but the upper (inner) side is slightly 

 hairy; the rounded, outer (upper) border of the palm bears a narrow, transverse groove, just 

 near the articulation of the dactylus, as in A. bidens, and this groove is not broader than the 

 base of the dactylus; inner or lower border of the chela rounded, straight and entire. Fingers 

 little more than half as long as the palm, dactylus compressed, slightly longer than the immobile 



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