PfeREZ FARFANTE: ROCK SHRIMP GENUS SICYONIA 



third occasionally projecting slightly or forming 

 small spine. Posteroventral extremity of pleuron 

 of first and second somites rounded, that of third 

 variably angular (sometimes bearing spine), and 

 that of fourth through sixth produced in caudally 

 directed spine. 



First somite marked with short anteromedian 

 pleural sulcus continuing as shallow depression to 

 near ventral margin of pleuron, and long, united, 

 posterior tergal-posteromedian pleural sulci. Sec- 

 ond through fourth bearing anterior tergal sulcus 

 (that of fourth weak or sometimes lacking), and 

 united posterior tergat-posteromedian pleural 

 sulci; second and third also bearing shallow 

 depression representing anteromedian pleural 

 sulcus. Fifth somite with almost indistinct an- 

 terior tergal and strongly arched, united posterior 

 tergal-posteromedian pleural sulci. Sixth somite 

 with arched posteromedian pleural sulcus barely, 

 if at all, distinct, and bearing well-marked, long 

 cicatrix. 



Telson with median sulcus deep basally, fading 

 posteriorly, and armed with small but well- 

 defined, fixed subterminal spines. Rami of uropod 

 subequal in length, exceeding apex of telson by as 

 much as 0.25 of their length. 



Posterior spine on first abdominal sternite 

 broadly subtriangular with blunt apex and 

 straight or usually convex, instead of concave, lat- 

 eral margins. 



Petasma (Fig. 59A,B) with cornified distal pro- 

 jection of dorsolateral lobule directed distolater- 

 ally, acutely pointed, ending in short filament, and 

 raised in proximodorsal, subhemispheric promi- 

 nence. Distal projection of ventrolateral lobule 

 reaching as far as projection of dorsolateral lobule, 

 mostly fieshy, blunt, and produced in small lateral 

 tooth just proximal to midlength. 



Petasmal endopods joined in males 10.5 mm cl, 

 about 41 mm tl, but in individuals with carapace of 

 as much as 19 mm, about 70 mm tl, they may not be 

 joined. 



Appendix masculina as illustrated in Figure 

 59C. 



Thelycum (Fig. 60) with plate of sternite XIV 

 bearing paired strong protuberances bordered lat- 

 erally by narrow flanges and separated by deep 

 median depression sharply delimiting their pos- 

 teromesial margins. Median plate of sternite XIII 

 flask-shaped in outline, tapering gradually into 

 long, slender spine reaching between base and 

 midlength of basis of extended second pereopods; 

 plate set off from posterior component by deep 

 incisions and usually raised posterolaterally in 

 paired rounded prominences flanking narrow de- 

 pression (narrower than prominences); posterior 

 component of median plate bearing paired strong, 

 short bosses separated by deep median depression, 

 each boss cut by transverse suture. Paired short 

 spines projecting anteroventrally from posterior 



Figure 59. — Sicyonia ingentis, i 16 mm cl, southeast of Punta Tasco, Isla Santa Margarita, Baja California Sur, Mexico. A, 

 Petasma, dorsal view; B, ventral view of same; C, right appendix masculina, dorsolateral view. Scale = 1 mm. 



71 



