P6REZ FARFANTE: ROCK SHRIMP GENUS SICYONIA 



anteromedian pleural sulcus short, extending 

 from slightly below midheight of somite to near 

 ventral margin; posteromedian pleural sulcus 

 with faint dorsal extension directed anteriorly at 

 about 0.33 height of somite from dorsomedian line 

 and just ventral to weak crescent- shaped ridge 

 (latter delimited dorsally by tergal sulcus). Fourth 

 somite with anterior tergal sulcus shallow and 

 posterior tergal and posteromedian pleural sulci 

 coalescent, extending from near base of dorsal 

 carina to curve anteriorly near ventral margin. 

 Fifth somite with united posterior tergal- 

 posteromedian pleural sulci ending well above 

 ventral margin. Sixth somite with strongly arched 

 posterior pleural sulcus and low longitudinal 

 ridge situated between base of middorsal carina 

 and setose depression lying dorsal to weak cica- 

 trix. 



Telson with very weak median sulcus and bear- 

 ing pair of small, fixed subterminal spines. Both 

 rami of uropod extending as far as apex of telson or 

 surpassing it by as much as 0.2 of their own 

 lengths. 



Petasma (Fig. 36A, B) with rigid distal projec- 

 tion of dorsolateral lobule curved mesially, raised 

 proximodorsally in rounded prominence, and 

 compressed distally; its truncate tip with ventral 

 extremity rounded and dorsal extremity acutely 

 produced in acute salient. Distal projection of ven- 



trolateral lobule fleshy, with terminal part flat- 

 tened (dorsal surface not bulbous) and curving 

 dorsally. 



Appendix masculina as illustrated in Figure 

 36C. 



Thelycum (Fig. 37) with plate of sternite XIV, 

 delimited by arched or straight lateral edges, 

 rounded anteriorly, its surface raised in low, ovoid 

 bulges separated by broad, median depression. 

 Median plate of sternite XIII flask-shaped in out- 

 line, tapering gradually into long, slender spine 

 reaching between midlength of coxae and proxi- 

 mal extremity of bases of second pereopods; plate 

 incised and excavate at level of coxae of fourth 

 pereopods; posterior component of plate with shal- 

 low posteromedian emargination. Sternite XI 

 armed with paired short spines. Posterior thoracic 

 ridge with concave anteromedian margin slightly 

 overlapping plate of sternite XIV, ridge then flush 

 with, or separated by shallow, transverse depres- 

 sion from sternite XIV. 



Color. — "...light greenish yellow, banded with 

 vermilion on the branchial regions and abdomen. 

 Appendages red, antennary flagellum trans- 

 versely banded with light and dark" (Faxon 

 1893). 



Maximum size. — In the meager material avail- 



FIGURE 36.— Sicyonia affinis,i 21.5 mm cl, 4.4 km off Isla Manuelita, Costa Rica. A , Petasma, dorsal view; B, ventral view of same; 



C, right appendix masculina, dorsolateral view. Scales = 1 mm. 



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