CRUSTACEA. 

 74 



corresponding nearly to Edwards's division "Lupees marchess." In 

 one specimen in our collections, this joint is tnangular and very 

 slightly longer than its breadth at base; in another it is considerably 

 Oblong with the summit truncate instead of obtusely pointed, and this 

 summit is bent a little outward and upward. Both of these species 

 have a long lateral spine, like that in A. hastaknJes of De Haan, 

 which they resemble, the same kind of teeth on the lateral margin, 

 similar frontal teeth and eyes. Indeed, in every essential point they 

 are congeneric. In another species (near A. gladiator, as figured by 

 De Haan, pi. 18, f. 1), this third joint of the outer maxillipeds is still 

 more oblong and concave on its surface, and is bent obliquely upward 

 and outward over the summit of the palpus, so as to present its surface 

 in this part to a front view, instead of its edge;— this peculiarity is 

 but a farther development beyond that in the second of these three 

 species alluded to. (See figures of these species, Plate 17.) Such 

 are the wide variations in the outer maxillipeds in species which give 

 no other grounds for generic distinctions. 



Again, De Haan makes Neptunus and Achelous differ from Amphi- 

 trite in having the third joint of the outer maxillipeds more oblong, 

 the reverse of which is actually the fact among many of the species 

 examined by us. So, in Thalamita, this same joint is described as 

 short, when, in fact, it is sometimes longer than broad. The form in 

 Thalamita inteejra scarcely differs in relative length or in obliquity 

 from that of Lupa dicantha. Again, Oceanus (Thalamita eruciteni 

 of authors), is said to have the inner branch of the first maxillipeds 

 trilobate; and Thalamita is described as having the same margin uni- 

 dentate. The latter has the inner lobe as in Oceanus; but the outer 

 is straight at top (as in Th. admetus), or concave in outline (as in 

 Th. crassimana and crenata), and this concavity is so deep and angu- 

 late in Thalamita integra that it approaches nearly the bilobate cha- 

 racter of Oceanus, although the integra is otherwise very near the 

 admetus. It seems evident, therefore, that too much importance is 

 allowed to small variations in these organs — the shape of the triangle 

 — its upper margin straight or sinuous, and the like; for such cha- 

 racters are of little value unless as indications or accompaniments of 

 other peculiarities. 



As an example of species having such accompanying characteristics, 

 we have, in a preceding paragraph, alluded to the genus Cancer. Eri- 

 phia affords another example; the form of the maxillipcd branch is 



