54 
THE VOYAGE OF H.M.S. CHALLENGER. 
parallel, or in contact to near their extremities, which are usually divergent. Orbits 
small, with a lateral aspect, with a hiatus above and below (sometimes with two hiatuses 
in the upper margin). Post-abdomen in both sexes distinctly seven-jointed. Eyes 
rather small, retractile, and when retracted, concealed within the orbits. Antennae with 
the basal joint considerably enlarged and usually armed with a tooth or spine at the 
antero-external angle, the flagellum exposed and visible in a dorsal view at the sides of 
the rostrum. Exterior maxillipedes with the merus-joint distally truncated, the antero- 
external angle considerably produced and rounded or subacute, the antero-internal angle 
slightly notched. Chelipedes (in the adult male) well developed, with the palms either 
turgid, fingers arcuate and meeting only at the distal extremity, or more slender, with 
the fingers nearly straight. Ambulatory legs of moderate length (the first much the 
longest) with the joints subcylindrical, without spines ; the dactyli short and nearly 
straight. 
In 1879 1 I proposed, in order to retain Leach’s designation Pisa for some of the 
species with which it had been generally associated, to use this term as a subgeneric 
designation for those species in which the carapace is more ovate in shape and the palms of 
the chelipedes (in the adult male) turgid, with the fingers strongly arcuated and meeting 
only at the tips ; but I doubt whether the characters are sufficiently constant and well 
defined even for this purpose. Of the described species of this genus, three, viz., Pisa 
tribulus (Linn.); Pisa hirticornis (Herbst) = Pisa corallina, Eisso, Pisa quadricornis, 
Brandt, var. and Pisa tetraodon (Pennant) = Pisa convexa , Brandt, inhabit the 
Mediterranean in water of moderate depth (70 to 75 mm., Pisa tribulus, A. Milne 
Edwards). Of these species, two, Pisa tribulus and Pisa tetraodon, range northward to the 
English and Irish coasts, and southward to the Azores and Tenerife (50 to 90 fathoms) ; 
Pisa tribulus to the Cape Verde Islands, 38 fathoms (Studer). There are also specimens 
of Pisa tetraodon and Pisa corallina from Aden in the British Museum collection. 
Another species, Pisa carinimanus, Miers, has been described from the Canaries and 
G-oree Island, Senegambia (9 to 15 fathoms). A species, Pisa brevicornis, A. Milne 
Edwards, occurs at Madagascar; and another, Pisa acutifrons, A. Milne Edwards, at 
Zanzibar. Three species, Pisa antilocapra, Pisa prolong a, Stimpson, and Pisa 
erinacea, A. Milne Edwards, occur in the Florida Straits or Caribbean Sea at depths of 
37 to 118 fathoms (the last-mentioned species should perhaps be referred to the genus 
Notolopas). 
1 Journ. Linn. Soc. Land. (Zool.), vol. xiv. p. 657, 1879. 
