FISHERY BULLETIN; VOL. 86, NO. 2 



ated with pereopods 1-5; smaller and more nearly 

 symmetrical U-branched arthrobranchs of more 

 nearly uniform size associated with third maxil- 

 liped and pereopods 1-4. 



Key to Known Species oi Alvinocaris 



1. Telson with terminal margin slightly con- 

 cave in midline and bearing 3-5 pairs of 



principal spines 



A. lusca Williams and Chace 



Telson with terminal margin convex and 

 bearing only 2 pairs of principal spines ... 2 



2. Rostrum with ventral margin bearing 0-1 



subterminal ventral spines 



A. stactophila new species 



Rostrum with ventral margin bearing 4 or 

 more subterminal ventral spines 3 



3. Abdominal segment 3 with pleural margin 

 entire A. markensis new species 



Abdominal segment 3 with pleural margin 



obscurely serrate 



A. muricola new species 



Alvinocaris markensis new species 



Figures 1, 2, 7 



Material— \JSnU 234286, Holotype 9 

 (crushed), USNM 234287, Paratypes, 2 9 (dam- 

 aged), Mid-Atlantic Rift Valley about 70 km 

 south of Kane Fracture Zone (see Leg 106 Ship- 

 board Scientific Party [1986]; Ocean Drilling Pro- 

 gram Leg 106 Scientific Party [1986]), 

 23°22.09'N, 44°57.12'W, 3,437 m, Alvin Dive 

 1683, MARK vent, Stn. 1, scoop, 30 May 1986, 

 pilot D. Foster, observers S. Humphris and J. Ed- 

 mond. From NSF Ocean Drilling Program-Leg 

 106, NSF Grant OCE-8311201 to J. F. Grassle, 

 Woods Hole Oceanographic Institution, Woods 

 Hole, MA. 



Measurements in mm. — Holotype 9, postor- 

 bital carapace length 4.16, rostrum 2.3, maxi- 

 mum carapace height 3.3, total length about 

 15.6. Paratype 9, same 2.7, 1.6, 2.4, 10.9. 



Description. — Integument extremely thin, 

 264 



membranous, shining, with a few minute puncta- 

 tions. Rostrum (Fig. la, 6) almost straight, 

 slightly elevated above horizontal in distal half, 

 sharply pointed tip usually reaching to between 

 midlength of second and tip of third peduncular 

 articles of antennule; dorsal margin raised into 

 thin serrate crest containing 12-17 teeth, 

 strongest in central sector of row, with about 1/3 

 length of crest continued onto carapace; ventral 

 margin less prominent and armed with 5-8 sub- 

 terminal teeth; tooth formulas examined, 17/8 

 (holotype), 17/5, 12/5 (apparently some subtermi- 

 nal dorsal teeth fused); strong lateral carina 

 broadened proximally and confluent with orbital 

 margin. Carapace with acute antennal spine dis- 

 tinct; pterygostomian spine acuminate and 

 prominent. Indistinct antennal groove curving 

 ventrad to intersect associated indistinct groove 

 at about midlength of carapace and continuing 

 posteriad. 



Abdomen of female (Fig. Ic) apparently 

 broadly arched dorsally (all specimens examined 

 are crushed), gradually tapering posteriorly, nar- 

 rowest part of sixth somite about 1/2 width of first 

 somite; pleura of 3 anterior somites broadly 

 rounded, that of fourth somite drawn posterolat- 

 erally to strong acuminate spine flanked dorsally 

 by or 1 much more slender and smaller spine; 

 posterolateral corner of fifth pleuron strongly 

 acuminate to nearly right angled and flanked 

 dorsally by 0-2 spines of variable size analogous 

 to condition on somite 4, spine number possibly 

 age related; sixth somite with middorsal length 

 about 1.9 that of fifth, broad based midlateral 

 spine overlapping base of telson, smaller pos- 

 terolateral spine acute; fourth somite with small 

 erect spine on sternite and fifth with analogous 

 strong, posteriorly directed spine. Telson (Fig. 

 \d) elongate subrectangular, length about 3.5 

 anterior width, 5.8 posterior width, and about 

 1.75 length of sixth somite, not including poste- 

 rior spines; armed with 6-8 dorsolateral spines 

 of nearly uniform size, sometimes bilaterally 

 unequal in number; posterior margin convex, 

 armed with 2 principal spines at each corner 

 and 10-12 feathered strong setae on margin be- 

 tween. 



Eyes (Fig. la , 6 ) with cornea imperfectly devel- 

 oped, unfaceted though diffusely pigmented, glob- 

 ular to ovate in outline and with prominent spine 

 on anterodorsal edge. 



Antennular peduncle (Fig. la, 6) reaching end 

 of antennal scale; basal article 1.3 length of sec- 

 ond and about 3.0 length of third, stylocerite well 



