FISHERY BULLETIN: VOL. 75. NO. 2 



ischium, and merus. Exopods on all maxillipeds 

 and pereopods. Lateral ramus of uropod armed 

 with distolateral spine reaching distal margin of 

 lamella (terminal spine). In males, petasma with 

 ventral costa free from heavily sclerotized, plate- 

 like terminal part of ventrolateral lobule; ventro- 

 median lobule broadly expanded distally. Endo- 

 pod of second pereopod bearing appendices 

 masculina and interna, and with basal sclerite 

 produced distally into elongate ventrolateral 

 spur. Thelycum of open type, not enclosing 

 seminal receptacle. Pleurobranchia on somites 

 IX to XIV; single rudimentary arthrobranchia on 

 VII, and anterior and posterior arthrobranchiae 

 on somites VIII to XIII; podobranchia on second 

 maxilliped, and epipod on second maxilliped (and 

 on first if proximal exite of coxa considered an 

 epipod) through fourth pereopod. 



Hadropenaeus is an extremely homogeneous 

 genus, the three known species being quite 

 similar. 



Type-species. -Hymenopenaeus modestus Smith 

 1885. 



Etymology. -From the Greek hadros, stout, in com- 

 bination with the generic name Penaeus, allud- 

 ing to the comparatively short and thick 

 carapace. 



Gercofer.-Masculine. 



List o/"spedes.-Amphi-Atlantic: Hadropenaeus af- 

 finis (Bouvier 1906b). Western Atlantic: Hadro- 

 penaeus modestus (Smith 1885). Indo-West 

 Pacific: Hadropenaeus lucasii (Bate 1881). 



Affinities. -The members of Hadropenaeus resem- 

 ble those of Pleoticus (as here defined) in having 

 the epigastric tooth separated from the first ros- 

 tral by an interval equal to, or only slightly 

 greater than, that between the first and second 

 rostral teeth, in lacking both branchiocardiac and 

 posthepatic carinae, and in possessing a petasma 

 in which the ventral costa is free from the plate- 

 like, terminal part of the ventrolateral lobule. 

 However, Hadropenaeus differs from Pleoticus 

 (as well as from the other closely related genera 

 except Mesopenaeus) in the proportionately 

 higher carapace, in the shape of the rostrum 

 which is short, deep, and possesses a strongly 

 convex ventral margin, and in lacking sub- 

 marginal carinae. 



316 



The members of this genus are closely allied to 

 those of Mesopenaeus. They share a stout appear- 

 ance, short, deep rostrum in which the ventral 

 margin is convex, similar arrangement of the 

 epigastric and rostral teeth, and they lack 

 branchiocardiac sulci and carinae. Furthermore, 

 the ventral flagellum, which is typically flattened 

 in Mesopenaeus, is occasionally depressed in one 

 species of Hadropenaeus; the depressed flagellum 

 seemingly represents the first step in a process 

 of specialization which progressed through the 

 flattened ventral flagellum in Mesopenaeus, and 

 culminated in the two lamellate flagella (both 

 ventral and dorsal) in Solenocera. Hadropenaeus, 

 in contrast to Mesopenaeus, lacks submarginal 

 carinae and orbital spines; it possesses branchio- 

 stegal spines and, most significantly, exhibits a 

 petasma in which the ventral costa is free from 

 the terminal part of the ventrolateral lobule. 



Key to Species of Hadropenaeus 



1. Rostrum lacking conspicuous carina dor- 



sal to adrostral one. Thelycum with 

 median protuberance on sternite XIV 

 high, projecting ventrally as far as 

 posterior convexities of sternite XIII; 

 latter with median ridge bearing large 

 tooth anteriorly. Petasma with ventro- 

 median lobule produced into disto- 

 lateral projection 2 



Rostrum with conspicuous carina dorsal 

 to adrostral one. Thelycum with me- 

 dian protuberance on sternite XIV 

 low, not projecting ventrally as far as 

 posterior convexities of sternite XIII; 

 latter with median, keellike ridge 

 lacking tooth anteriorly. Petasma 

 with ventromedian lobule not pro- 

 duced into distolateral projection .... 

 H. lucasii 



2. Scaphocerite reaching distal end of an- 



tennular peduncle or overreaching it 

 by not more than 0.1 of its own length. 

 Prosartema extending only to disto- 

 mesial extremity of first antennular 

 article. Thelycum with median pro- 

 tuberance on sternite XIV projecting 

 ventrally, and tooth of median keel of 

 sternite XIII directed anteriorly. Pe- 

 tasma with distomesial projection of 



