DESCRIPTION OF SPECIES 325 



third to the fifth somites being separated by sutures. The coxal plates are sickle-shaped, 

 with the terminal portions from the articular processes outwards, curved first forwards 

 and then outwards, so that a space is left between two consecutive plates. Those of the 

 seventh somite are produced backwards to near the end of the terminal segment in the 

 male, and to about the level of the base of the terminal spine in the female. 



The first three abdominal segments are sub-equal (Fig. 13 b), each a little more than 

 half the length of the thoracic somites. The pleural plates of the second and third seg- 

 ments are long, narrow and produced backwards beyond the point of attachment of the 

 uropod, those of the second being slightly the longer : the outer margins of the coxal and 

 pleural plates are serrated. In the female the sterna of the first three abdominal seg- 

 ments each have their posterior margin produced into a median spine which is largest 

 on the third segment; these are hardly developed in the male. 



The terminal segment (Fig. 13 6) is pentagonal in outline, slightly longer than broad, 

 terminating in a long spiniform process which is slightly upturned ; on its dorsal surface 

 is a median dorsal keel bearing five large spines directed upwards and slightly back- 

 wards, and decreasing in size from before backwards. The area in front of the first spine 

 is raised and bears two small spines, from the base of each of which a transverse oblique 

 carina extends outwards to near the lateral margin where it ends in a sharp backwardly 

 directed spine. The margin between the attachment of the uropod and the terminal 

 spine is sharply serrated. 



Remarks. As the descriptions of the mouth-parts and appendages given by Studer 

 (1879, PP- 21-24) are very brief, some further details are given here. The appendages 

 are all of the normal type and bear a very close resemblance to those of S. trilobitoides. 

 Eights. The antennule and the antenna are described by Studer, but he failed to observe 

 that a dorsal groove is present on each of the first three peduncular joints of the former, 

 and of the second to fifth joint of the latter. The surface of each groove, like that of 

 S. trilobitoides, is covered by short setae which are all directed towards the centre of the 

 groove in a distal direction. The number of joints in the flagella of both antennule and 

 antenna appears to be greater than that given by Studer ; his number for the former is 

 twenty-two and for the latter fourteen, whereas in specimens in the present collection 

 these numbers are increased to thirty and eighteen respectively. A further detail 

 omitted from Studer's description is the mention of the row of teeth occurring on the 

 ventral surface of the middle joints of the flagellum of the antenna : these are also seen 

 in a corresponding position in S. trilobitoides and were figured by Beddard (1884&, pi. i, 

 fig- 6). 



The cutting edges of the mandibles are strongly chitinous : their form is shown in 

 Fig. 13 c. The outer lobe of the maxillula (Fig. i a) bears nine strong spines and an inner 

 pectinate seta on its distal extremity. The inner lobe is broad distally, with a series of 

 extremely small toothed spines on the outer margin of its rounded end, and a single 

 longer spine near its inner margin. There are two setae, on both the inner and outer 

 lobes of the left maxilla (Fig. i c), whilst on the right there are two on the outer and 

 three on the inner lobe : the fixed lobe of both bears about thirty setae. 



