List of Species 



P. {M.) hrerlrostris Kinofsley and P. {M.) rnll- 

 fomiensis Holmes from the eastern Pacific; P. 

 (M.) azf ecus astecus Ives, P. (31.) aztecus subtUis 

 Perez Farfante, P. {M.) patdcnsis Perez Farfante, 

 P. (J/.) hnisih'ensis Lat., P. (M.) duoranan 

 duorarum Burkenroad, and P. (31.) duorarum 

 nofialis Perez Farfante from the western Atlan- 

 tic — the last-named subspecies from the eastern 

 Atlantic (West Africa) also; P. (31.) kerathu?m,s 

 (Forskal) from the Mediterranean Sea and eastern 

 Atlantic ;F. (31.) Jafi.sidcafu.sKhh'moiiye^P. (31.) 

 longistyhis Kubo, P. (31.) marginatus Eandall, 

 P. (31.) pJehejus Hess, and P. (31.) teraoi Kubo 

 from the Indo-Pacific; and P. (31.) japonicus 

 Bate ('i = P. (31.) ranaJ iciilaf us OViviev) from the 

 Indo-Pacific and eastern Mediterranean Sea. 



The list of Indo-Pacific species follows the con- 

 clusions of Hall (1962) and Eacek and Dall 

 (1965), as well as previous opinions by Kubo 

 (1949), Holthuis (1949), and Dall (1957). 



Remarks on Subgenera 



The five species of the subgenus Litopenaeus are 

 restricted to American \yaters and differ markedly 

 from other members of the genus in characters of 

 the external genitalia which neither Burkenroad 

 (1934) nor Kubo (1949) took into account when 

 they recognized species groups of the genus 

 Penaeus. In respect to both the thelycum and the 

 petasma, these species are more primitive than the 

 species of the other subgenera. The open thelycum, 

 which is obviously less specialized than the closed 

 type, has only ridges and protuberances for the 

 fastening of the spermatophores, which are left 

 exjDosed. In Litopenaeus the spermatophores have 

 strong structures for attachment to the thelycum, 

 whereas in the remaining species these structures 

 seem to be represented — as suggested by Burken- 

 road (1934) — by vestigial processes. Only one 

 species with a closed thelycum (P. japonicus) has 

 spermatophores with large processes (Tinuizi, 

 1958), but the processes differ from those in the 

 species with an open thelycum. The lack of a 

 gastrofrontal carina and the possession of a hepatic 

 carina seem to be primitive. 



Since the species of the genus Litopenaeus ap- 

 pear to be more primitive and are restricted to 

 American waters, I agree with Burkenroad (1934) 

 that the genus could well have originated in the 

 Western Hemisphere. 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEUS 



The remaining species of Penaeus have a closed 

 thelycum, which possesses two flaps that occur as 

 "lateral plates" on the ventral surface of sternite 

 XIV ; the lateral plates are separated by a median 

 slit that opens into a seminal receptacle dorsal to 

 and continuous with the lateral plates. P. japonicus 

 provides an exception in having a poucMike 

 thelycum with an anterior oj^ening on sternite 

 XIV. 



Penaeus s.s. is apparently the more primitive of 

 the groups of species with a thelycum of the closed 

 type, sharing with Litopenaeus the sculpture of the 

 carapace, including a well-developed hepatic 

 carina. Kubo placed the species of Litopenaeus and 

 Penaeus s.s. together in his subdivision 2. 



Fenneropenaeus differs from Penaeus s.s. in 

 lacking a hepatic carina or, in one species (P. 

 peniciUatus) , having only a barely noticeable one; 

 the character seems to have been secondarily lost. 

 The absence of this carina in most species of 

 Pe7\aeus s.s., and the shallow adrostral sulcus and 

 posteriorly attenuated adrostral carina indicate a 

 tendency for the carapace to become smoother. 



There is little doubt that Melicertus includes the 

 most advanced group of species; the long adros- 

 tral sulcus and carina appear late in development, 

 at the beginning of the juvenile stage. 



Key to the Western Atlantic Species of 

 Penaeus 



1. Adrostral sulcus short, extending to epigastric 



tooth; gastrofrontal carina absent ("non- 

 grooved shrimps") 2 



Adrostral sulcus long, extending posteriorly 

 beyond epigastric tooth ; gastrofrontal carina 

 present ("grooved shrimps") 3 



2. Petasma with distal portion of lateral lobe bear- 



ing diagonal ridge on inner surface, and distal 

 ventromedial corner rounded. Thelycum with 

 anterolateral ridges turned mesially and pair 



of fleshy protuberances on sternite XIV 



P. (L.) setiferus (L.) (p. 468) 



Petasma with distal portion of lateral lobe lack- 

 ing diagonal ridge on inner surface, and 

 distal ventromedial corner produced in sub- 

 rectangular projection. Thelycum with sub- 

 parallel anterolateral ridges, never turned 

 mesially, and pair of rounded and rigid pro- 

 tuberances on sternite XIV 



P. (L.) sclimitti Burkenroad (p. 487) 



3. Petasma with distomedian projection long; dis- 



tal fold intruding considerably inside petasma 



467 



