3G8 KIll'OItT OF COMMISSION Kll OF FIHIF AND FTR1TERIES. 



Sphaeroma l,:ilrrillo. 

 H/ilnrroina Laf roillo, llisl. naL. drw CnisL nt dcs IIIH., lomo vii, ]>. 11, 1804. 



Body contractile into ;i, sphere; antemmhe and antenna', short or of 

 moderate length; maxillipeds with a live jointed palpus; legs all ambu- 

 liilory; daclyli short and thick ; nropods short, rainns and basal seg- 

 ment siibeqiial. 



The, name of this genus is derived IVom the peculiar habit, of many 

 Of the Species Of rolling themselves into a, ball when alarmed. The, body 

 is so constructed as l,o I'aeililate tin's operation, the antennnhc and 

 antenna) being received into a groove at the, side of the. head; the cpi- 

 meral regions of the, thoracic segments behind the first are, narrowed 

 nearly to a point and project well downward so as to moot very close 

 together and still leave room for the included legs, while t lie nropods, 

 shutting together like a pair of scissors, ibid also partly under the largo 

 terminal segment of the, pleon and till the crevice between tin- pleon and 

 the head. The maxillipeds in this genus are provided with a long 

 densely ciliated live-jointed palpus. The, maxill;u are much as in the 

 Idotcidcc, the outer pair three-lobed and strongly ciliated, the inner 

 two lobed with the inner lobe small and tipped with pectinate seta 1 , the 

 outer larger and armed with curved denticulated spines. The mandibles 

 have, a strong molar process, a dentigerous lamella armed with acute 

 teeth, and a throe-jointed palpus. 



The, legs are rather weak and nearly alike throughout, all ambulatory. 

 The, pleon is scarcely narrower than the segments of the thorax and ap- 

 pears to consist of two* segments only, of which the first is much like the 

 last thoracic segment, but more strongly produced at the sides than is 

 that segpient and marked with impressed lines. It is articulated with 

 considerable motion to the large scutiform terminal segment, which, in 

 this genus, is rounded and entire at the lip, and not strongly tubercu- 

 lated nor spiny. Anteriorly, the angles of this segment are, produced 

 downward into a rounded lobe in front of the shoulder from which arise 

 the nropods. These organs are not greatly elongated ; the basal seg- 

 ment is produced into a plate about equal in si/e to the single ramus. 



Sphaeroma quadridentatum Say. 



flphatroma qiindridcnlnla Say, Jour. Acad. Nat. Sci. Phil., vol. i, p. 400, 1818. 

 Dokay, Zool. Now York, Crust., p. -14, 1HM. 

 Whito, Lint Criwfc. Brit. Mus., p. HfcJ, fH47. 

 Harder, Am. .lour. Sci. ,111, v., p. :'.! 1, |H~:5; This Report, parti, p. 569 



(275), pi. v., fig. 21, 1874; Proc. U. S. Nat. Museum, 1879, vol. ii, p. 161, 



1879. 

 Von-ill, This Report, part, i, p. :Uf> ('21), 1H74. 



PLATH IX, FIG. 53. 



The outline of the body when extended is a pretty regular ellipse, but 

 the animal, when disturbed, rolls itself into a ball with facility, and by 



*Tlio pleon is iiuulverUmUy iloscrilxnl l>\ l!:i,l,o :m<l Wc.sl xvood in Ilio British Sossilo- 



Eyed Crustacea, vol. ii,p.4()l, as "having all MIO segments fused together." 



