THE SPIDER CRABS OF AMERICA 465 



The carapace is very little, sometimes not at all, constricted behind 

 the orbits. 



The posterior median spine varies in the three scries in a manner 

 similar to that seen in the lateral spines. 



In series 1, the four large tubercles or bosses about the middle 

 of the carapace (one gastric, one cardiac, two branchial) are very 

 prominent, and some or all of them have an acute tip, that on the 

 gastric boss occasionally resembling a short spine; in series 2, the 

 bosses run lo\yer and there is a tendency to form a sharp tubercle 

 or granule at the summit of the gastric boss; in series 3, the bosses 

 are still lower and arc smoothly rounded and blunt. 



Within each series there is great diversity in the length, direction 

 and curvature of the rostral horns. The length varies from one- 

 fifth to over one-third of the length of the remainder of the carapace. 

 The horns may be straight, with their outer margins subparallel 

 (19584, 21930), or converging distally (46915) and the interspace 

 insignificant in the basal half. They may curve strongly outward 

 or upward or both (17959, 50956) toward the tips, and be either 

 almost contiguous at base (43028) or have a narrowly U-shaped 

 interspace (9279, 9280, 15137). This interspace may be regularly 

 V-shaped or nearly so (14004, 46925). 



The orbits in series 1 are very prominent, owing to the constriction 

 of the carapace behind them, the upper edge is deeply emarginate, 

 the preocular and postocular teeth strongly marked, the former 

 directed forward and curved. In series 2, the superior emargination 

 of the orbit is less deep, the teeth less strongly marked, although 

 the preocular tooth is directed forward and a little curved. In 

 series 3, the orbit has a very slight emargination in the upper border, 

 the preocular tooth is acute but not prominent, the postocular angle 

 is blunt or subacute but not dentiform in the old; both preocular 

 and postocular teeth incline to greater prominence in the young. 



Nomenclature. — The earliest record of this species was made in 

 1756 by Browne, who called it ^^ Cancer 9. The Grass-Crab." 

 There is nothing in his brief diagnosis to indicate which of the three 

 forms described above he had in hand; his figure, however, has 

 very slender postero-lateral spines, as in series 1. Latreille (1825) 

 was the first to give a specific name to the species, Pisa trispinosa; 

 his description also applies to series 1, "trois elevations en forme de 

 petites bosses, terminees en pointe, le long du milieu du dos; * * * 

 angles posterieurs prolonges en une Spine tre-forte." The locality 

 "Nouvelle Hollande?" is an error, which was corrected later (1834) 

 by Milne Edwards. In the mean time another record of the same 

 form, typical Pisa trispinosa, was made by Guerin in his "Icono- 

 graphie," where the slender postero-lateral spines are again shown. 

 Unfortunately A. Milne Edwards gave another specific name, 



