LEPTOSTRACA. SYNCARIDA. 459 



gland in the basal joint of the second antenna, but also by a 

 much reduced shell gland connected \\ith the second maxilla. 



The tubular heart extends through the thorax and part of the 

 abdomen ; it possesses four large and three small pairs of ostia. 



The testes and ovaries are long tubular structures lying parallel 

 to the intestine. The vas deferens opens on the coxal joint of 

 the last thoracic appendage, and the oviduct was believed by 

 Claus to open on the sixth thoracic segment. 



The males differ from the females by their more slender 

 form, the more abundant sensory hairs on the first antennae, 

 the long flagellum of the second, and the longer caudal appen- 

 dages. The eggs are carried by the female between the thoracic 

 appendages, and undergo a partial segmentation. A three- 

 limbed (nauplius) stage has been shown by Metschnikoff to 

 exist in their development, but they are hatched almost in the 

 form of the adult. 



The Silurian family, Ceratiocaridae, resembled the Leptostraca 

 in the possession of a bivalve shell, and the peculiar movable 

 head plate, but their organization is too imperfectly known in 

 other respects to establish the relationship. 



Family Nebaliidae. Nebalia Leach, widely distributed, British ; 

 Nebaliopsis G. O. Sars, blind or nearly so, from deep water, Southern 

 ocean ; Paranebalia Claus, Bermudas ; Nebaliella Thiele, eyestalks 

 developed, but without lenses or pigment, thoracic legs without epipodites ; 

 shallow water, Kerguelen I. and N. Zealand. 



Division 2. EUMALACOSTRACA. 



Malacostraca with seven abdominal segments including the 

 telson. They are without a shell muscle, and without a caudal 

 fork in the adult. . 



Order 1. SYNCARIDA. Packard.* 

 Malacostraca without a carapace, and with all the thoracic 



* Packard, A. S. On the Syncarida, Mem. Nat. Acad. Sc. Washington, 

 iii (2), 1886. Thomson, G. M. On a Freshwater Schizopod (Anaspides) 

 from Tasmania, Trans. Linn. Soc., Zool. vi (1893), p. 285. Caiman, W. T. 

 On the Genus Anaspides, Trans. R. Soc. Edinburgh, 38, pt. iv (1896), p. 

 787. Id. on the Classification of the Crustacea malacostraca, Ann. and 

 Mag. of N. H., sec. 7, xiii (1904), p. 144. Id. On the Characters of the 

 Crustacean Genus Bathynella Vejd.,Journ. Linn. Soc., Zoology, vol. xxvii 

 (1899), p. 338. 



