664 



PROCEEDINGS OF THE NA TIONAL MUSEUM. 



VOL. XXVII. 



hook-shaped, directed upvard and forward, one on either side of the 

 head. In the median excavation of the frontal margin on either side 

 of the median line is a prominent tubercle. Between the eyes and in 

 line with them on the posterior portion of the head are two low 

 tubercles. The eyes are situated at the extreme lateral margins on 

 the posterior portion of the head, and are somewhat elevated above 

 the surface; they are black and conspicuous, and 

 composed of many ocelli. The first pair of an- 

 tenna? consist of four joints, the last joint being- 

 clavate and fringed with hairs; the second pair 

 of antennte have a five-jointed peduncle, and a 

 flagellum composed of eight joints; the third 

 joint of the peduncle has a prominent tubercle. 

 The first four segments of the thorax are 

 longer than the last three. The lateral parts of 

 all the segments are widely expanded, with mar- 

 gins well rounded. The lateral parts are not 

 separated from the dorsal portion of the seg- 

 ments, but are firmly anchylosed. 



The abdomen consists of one segment, with 



suture marks, one on eithep side, indicative of 



another partly coalesced segment. The abdomen 



tapers gradually to a broadly rounded extremity, 



which is slightly excavate in the median line. 



The seven pairs of legs are but sparingly furnished with hairs. 



The upper half of the opercular valve is black, the lower half yellow. 



There are three longitudinal lines of low swellings on the bod}-, one 



median, the other two placed one on either side of the median line. 



Only one specimen was taken at Lands End, California, by Dr. 

 Ritter and party. 



This species is closely allied to Synidotea consolidata (Stimpson),* 

 but differs from that species in the 

 shape and greater size of the tubercles 

 in front of the e^^es, the tubercles 

 being hook-shaped and very prominent 

 in S. r^V/'e/'/ and projecting far in front 

 of the anterior margin of the head, 

 while in ,6'. consolidata they are small 

 (Stimpson speaks of them as being minute), are not hooked, and do 

 not project an}^ considerable distance in front of the anterior margin 

 of the head; in the greater size of the two median tubercles on the 

 anterior division of the head (Stimpson does not mention these tuber- 

 cles in his description, but in the specimens sent to the U. S. National 

 Museimi from Pacific Grove, California, by Mr. J. O. Snyder, and which 



Fig. 4.— Synidotea ritteri. 

 xlO. 



Fig. 5.— Head of (a) Synidotea ritteri 



AND of (b) S. CONSOLIDATA. X 10. 



«Proc. Cal. Acad. Sci., I, 1856, p. 97; Bost. Journ. Nat. Hist., VI, 1857, p. 503. 



