COPEPODA 141 



right side of the vulva, as well as by the frontal keel and by the teeth on the second basipodite of 

 the fourth pair of legs. 



This species is even more related to two newly established species, but if the descriptions are 

 correct, it is scarcely identical with them. 



From U. intermedia, which was described by A. Scott (1909 p. 63 — 64; PI. 23 figs 1—8), it differs 

 by a distinctly raised forehead between the rostrum and the keel, by the different shape and direction 

 of the two characteristic spines of the genital somite, as well as by a few other characters. From Wolf- 

 en den's Mesu7ideuch<£tc assymmetrica (191 1 pp. 244 — 245; Taf. 29 figs 4 — 7; text-fig. 28) from the Soil th 

 Atlantic, which it is very much like in dorsal view, it differs by the structure of the vulva, as the 

 right spine is wanting in Wolf en den's species. To encompass these species he established a new genus 

 on account of the teeth of the posterior surface of the second basipodite of pes IV; as the presence 

 of such spines (cf. Aetidius PI. II fig. i c), even if they are often wanting, is a rather characteristic 

 feature in the Aetidiidac, and as such spines are found in U. major as well, the foundation is rather 

 too weak. When all the structural features of males as well as of females are taken into consideration, 

 it is quite evident that the five species go naturally together. 



40. Chirudina Streetsii Giesbr. 

 (PI. V figs 4a-f; PI. VIII figs, sa-b; text-figs 38 a— k.) 



1906. Chirudina Streetsii Giesbr. Pearson, p. 16. 



1906. — — — Esterly, p. 59, pis 9, 10, 12, 14. 



1908. — — — Farran, p. 37. 



1908. — — — V. Bremen, p. 46. 



1909. — _ _ A. Scott, p. 43, pi. XII figs 



I — II. 



1513. — — — Wolfenden, p. 241. 



1895. Chirudina Streetsii n. sp. Giesbrecht, pp. 249—250; taf. i 



figs 5 — 10. 

 1898. — — Giesbr. Giesbrecht & Schineil, p. 34. 



1902 nee. Euchirella carinata n. sp. Wolfenden, pp. 366—367. 

 1904? — — Wolf. Wolfenden, pp. T15 — 116. 



1904. Chirudina Streetsii Giesbr. Cleve, p. 187. 



1905. — — — G. O. Sars, p. 4. 



Description, f?. Size of specimen from Thor St. 72 was 5-22 mm.; anterior division 4-18; uro- 

 some 1-04 mm. Giesbrecht's specimens measured 5-3 mm. Scott's specimens measured 4-8— 53 mm. 



The frontal keel and rostrum are well developed, as seen in text-fig. 38 a; dorsally there is trace 

 of articulation between the head and the first thoracic somite; the fourth and the fifth thoracic tergites 

 are completely fused, except dorsally, where trace of segmentation may be found. The lateral corners 

 vary very much in the different specimens; they are more or less rounded, but mounted with a pointed 

 process, which is sometimes almost wanting, especially on the right side (text-figs 38 b— e), but is some- 

 times well developed. The genital somite is in dorsal view slightly asymmetrical, as the right outline 

 is more regularly rounded than the left; the genital area (fig. 4 a), looked at from beneath, is very similar 

 to that of C. pustulifera, but observed from the side, a fairly prominent anterior protuberance and a 

 short, sometimes completely covered, posterior one are seen. 



The antennulae extend about to the base of the furcal branches; the segment 19, which is the 

 longest segment, is about 11 as long as 20, which is again longer than 17, the latter being about 

 II as long as 16; the segment 16 is ri as long as 24^^25. The exopodite of the antennae is 1-5 

 as long as the endopodite; the second segment of the endopodite has 7 + 7 setae; the first segment 

 of the exopodite, which is well defined and about one third as long as the second, has a well devel- 



