368 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



Spheeroma Latreille. 

 Sphceroina Latreille, Hist. nat. des Crust, et des Ins., tome vii, p. 11, 1804. 



Body contractile into a sphere ; antennulse and antennae short or of 

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

 latory ; dactyli short and thick ; uropods short, ramus and basal seg- 

 ment subequal. 



The name of this genus is derived from the peculiar habit of many 

 of the species of rolling themselves into a ball when alarmed. The body 

 is so constructed as to facilitate this operation, the antennulae and 

 antennae being received into a groove at the side of the head; the epi- 

 meral regions of the thoracic segments behind the first are narrowed 

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

 together and still leave room for the included legs, while the uropods, 

 shutting together like a pair of scissors, fold also partly under the large 

 terminal segment of the pleon and fill the crevice between the pleon and 

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

 densely ciliated five-jointed pali)us. The maxillse are much as in the 

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

 two-lobed with the inner lobe small and tipped with pectinate setae, the 

 outer larger and armed with curved denticulated spines. The mandibles 

 ha^^e a strong molar process, a dentigerous lamella armed with acute 

 teeth, and a three-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 segment and marked with impressed lines. It is articulated with 

 considerable motion to the large scutiform terminal segment, \yhich, in 

 this genus, is rounded and entire at the tip, 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 uropods. These organs are not greatly elongated ; the basal seg- 

 ment is produced into a plate about equal in size to the single ramus. 



Sphaeroma quadridentatum Say. 



Sjjliceroma quadridentata Say, Jour. Acad. Nat. Sci. Phil., vol. i, p. 400, 1818. 

 Dekay, Zool. New York, Crust., p. 44, 1844. 

 White, List Crust. Brit. Mus., p. 102, 1847. 



Harger, Am. Jour. Sci., Ill, v., p. 314, 1873; This Report, part i, p. 569 

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

 1879. 

 Verrill, This Report, part i, p. 315 (21), 1874. 



Plate 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 



* The pleou is inadvertently described by Bate and Westwood in the British Sessile- 

 Eyed Crustacea, vol. ii, p. 401, as "having all the segments fused together." 



