CRUSTACEA MALACOSTRACA. II. 



immature specimens of both sexes proves that adult males must be either very rare or, and 

 much more probably, that they swim about and are therefore rarely taken with the trawl or the 

 dredge. 



Immature or subadult males of many species were taken together with the females. In all species 

 with the pleopods quite rudimentary or wanting in full-grown females with or without marsupium 

 such subadult males are instantly recognized by having moderately developed or even somewhat large 

 pleopods; this is the case in several species of Leptognathia, in Pseudotanais forcipatiis and P. Lillje- 

 borgii, in Agathotanais, Leptognathiella, Strongylura, Paranarthrura. In all these forms the subadult 

 males have the abdomen proportionately either a little or. as in Paranarthrura insignis n. sp., consid- 

 erably longer than the female. In the genera with the antennulse four-jointed these appendages, and 

 especially their two proximal joints, are generally conspicuously thicker in the subadult males than in 

 the females, and in some species of Leptognathia (f. instance L. armata n. sp.) the antennulse of the 

 subadult male are five-jointed, as the fourth joint has its basal part marked off by an articulation. 

 In species of Pseudotanais or Leptognathia with the pleopods well developed in the female and in all 

 species of Typhlotanais the antennulse alone afford readily distinguishable differences between females 

 without marsupium and subadult males. In Typhlotanais the main difference is the thickness of the 

 two proximal joints and of a portion of the third joint; in Pseudotanais we find generally the basal 

 part of the third antennular joint somewhat thickened and besides protruding below. 



It is a common rule that when a good material of full-grown females of a species is to hand, 

 the great majority are without marsupium, even when taken at the same station. But it is a curious 

 fact that in several cases some of the largest specimens without marsupium are a little longer than 

 the longest specimen with marsupium; this fact I cannot explain, but I am induced to think that 

 some reduction in size may accompany the development of the marsupium and the eggs. In females 

 with marsupium the ventral surface of the lamelligerous or of all thoracic segments is rather or quite 

 flat, in specimens without marsupium most frequently considerably convex, but specimens without 

 marsupium are sometimes found showing the ventral surface flat and on the whole showing an 

 appearance as if the marsupial lamellse had been lost, but whether this has been the case is imposs- 

 ible to decide. 



In females without marsupium and subadult males of several species of Typhlotanais and of 

 Leptognatliia vcntralis n. sp. the second thoracic segment is below, and generally at or not very far 

 from the front ventral margin, produced in a generally acute and sometimes large process directed 

 downwards and more or less forwards; in females with marsupium and in very few cases in female 

 specimens without marsupium (perhaps lost) but with the lower side of the thoracic segments nearly 

 or quite flat this process is either reduced in size and shape (Leptognathia ventralis) or lost (Typhlo- 

 tanais). In Typhlotanais microcheles G. O. Sars females without marsupium and with the ventral 

 side of the thoracic segments convex, the ventral process is found on all thoracic segments excepting on 

 the seventh (vid. "Remarks" on T. gracilipes n. sp.) - In Paranarthrura insignis n. gen., n. sp., the 

 females without marsupium and subadult males have a conspicuous process on the ventral side of all 

 thoracic segments, but in females with marsupium only the process on the seventh segment has 

 been preserved. 



