and, insofar as ix)ssible, they ai-e correlated with 

 tlie geographical distribution of each animal. In 

 the study of variation, I considered 40 characters 

 other than those of the external genitalia. Tliose 

 charactei-s found to be of value are treated in the 

 text and in figures and gi-aphs. Data on color, size, 

 and sex differences in size are presented. A survey 

 of work on tlie biology and systematics of each 

 taxon is also included. Until 1936-39 only five 

 species were known to occur in the region. In 1967, 

 I described one new species and two new subspecies 

 from tlie western Atlantic. 



Particular attention has been accorded the de- 

 velopment of the systematic charactei-s of the 

 juveniles of each taxon. A description is given of 

 the progressive changes in the cle\^elopment of the 

 external genitalia which will aid in the identifica- 

 tion of juveniles. The size range at wliich each 

 taxon reaches the subadult stage, or at which the 

 external genitalia attain adult form, has been 

 detennincd. 



Geographic and bathymetric ranges are derived 

 from published data as well as material I exam- 

 ined. The commercial importance of each kind of 

 shrimp is summarized. Comments on the systemat- 

 ics, interrelationships of the various taxa, items 

 of special interest, and discussion of specific prob- 

 lems conclude the presentation. 



The morphological nomenclature I adopted is, 

 for the most part, that of Kubo (1949). A few 

 slight modifications were mad© for tlie sake of 

 brevity and clarity. For example, the lobules of the 

 petasnia are given single names — doi-somedian 

 ventromedian, doi-solateral, and ventrolateral — to 

 avoid such unnecessarily long wording, as, for in- 

 stance, "ventral lobule of lateral lobe" ; the "thick- 

 ened ventral margin of the petasnia" is called the 

 ventral costa ; and the two parts of the median pro- 

 tuberance of the thelycum are called the anterior 

 and posterior processes. "Whereas most previous 

 investigators recognize "proximal" and "distal" 

 pieces of the appendix masculina, it seems to me 

 that the so-called proximal piece is only a modifi- 

 cation of the endopod of the seconcl pleopod; 

 therefore, the "distal piece" appears to Ije equiva- 

 lent to what in other decapods is called the api>en- 

 dix masculina. For this reason "appendix mascu- 

 lina" as used herein is the "distal piece" of other 

 authors. A definitive terminology for the external 

 genitalia, however, must await further study of 

 their development and a demonstration of their 

 iiomologies. 



The measurement of total length is the distance 

 from the tip of the rostrum to the 2>osterior end 

 of the telson, and that of the carapace is the dis- 

 tance from the dorsal i^ortion of the postorbital 

 margin to the midposterodorsal margin of the 

 carapace. The latter dimension is accurate to 0.5 

 mm. In the text total length, carapace length, and 

 rostrum length are often abbreviated t.l., c.l., and 

 r.l., respectively. The citations to figures in the 

 references listed for each taxon have been restrict- 

 ed to those illustrating morphological characters; 

 other figures appear in the pages cited. 



GENUS PENAEUS FABRICIUS 



Penaem Fabricius, 1798: 408 (type species, by 

 subsequent designation of Latreille, 1810, 

 Penaeu.^ monodon Fabricius; neotype for 

 Pena-euii monodon, designated by Holthuis, 1949, 

 $ , Leiden Museum) ; Latreille, 1802: 246-250 

 Latreille, 1806: 53, 54; Latreille, 1810: 102, 422 

 Heller, 1863: 292, 293; Smith, 1882: 92-95 

 Smith, 1885 (not 1886 as is commonly stated) 

 170, 171; Bate, 1888: xii, 229-230 [part]; de 

 Man, 1911 : 95-97; Balss, 1914: 13; Burkenroad, 

 1934: 73-77; Anderson and Linchier, 1945: 302; 

 Kubo, 1949: 268-270; Dall, 1957: 140-142; 

 Gunter, 1957 : 98. 



Pencus Weber, 1795: 94 (nomen nudum. Opinion 

 104, International Commission on Zoological 

 Nomenclature); Philippi, 1840: 190; Smith, 

 1869a: 27; Smith, 1869b: 390; Alcock, 1901: 

 12-14; Alcock, 1905 : 510-515. 



MeUcertus Kafinesque, 1814 : 22. 



Penecus H. Milne Edwards, 1837 : 414. 



Penoeus Lucas, 1840 : 195, 196. 



Panem Collins and Smith, 1892 : 102. 



Panaeus Thallwitz, 1892 : 3. 



Diagnosis 



Rostrum usually with ventral teeth. Carapace 

 without longitudinal or transverse sutures; cervi-' 

 cal and orbito-antennal sulci and antennal carinae 

 always present. Hepatic and antennal spines pro- 

 nounced, pterigostomial angle rounded. Longitu- 

 dinal ridge of side of sixth abdominal somite 

 interrupted. Telson with deep median sulcus, with- 

 out fixed subapical spines, with or without lateral 

 movable spines. Fir.st antennular segment without 

 spine on ventral distomedian border. Antennular 

 flagella usually shorter than carapace. Palp of first 

 maxilla with two or three segments, usually three. 



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