THE MALACOSTRACA 149 



DIVISION 2. PERACARIDA, Caiman (1904). 



Carapace, when present, leaving at least four of the thoracic somites 

 distinct ; first thoracic somite always fused with the head ; protopodite 

 of antenna typically of three segments; mandible with lacinia mobilis 

 (except in parasitic and other modified forms) ; thoracic legs flexed 

 between fifth and sixth segments ; oostegites attached to some or all of 

 the thoracic limbs in female, forming a brood-pouch ; no appendix in- 

 terna on pleopods ; hepatic caeca few and simple ; heart generally 

 elongated, extending through the greater part of thoracic region, or 

 displaced into abdomen ; spermatozoa generally filiform ; development 

 taking place within the brood-pouch, young set free at a late stage. 



DIVISION 3. EUCARIDA, Caiman (1904). 



Carapace coalescing dorsally with all the thoracic somites ; eyes 

 pedunculate ; protopodite of antenna with, at most, two distinct seg- 

 ments ; mandible without lacinia mobilis in adult ; thoracic legs flexed 

 between fourth and fifth segments ; no oostegites ; an appendix interna 

 sometimes present on pleopods ; hepatic caeca much ramified heart 

 abbreviated, thoracic ; spermatozoa spherical or vesicular, often with 

 radiating appendages ; development as a rule with metamorphosis, a free- 

 swimming nauplius stage in the more primitive forms. 



DIVISION 4. HOPLOCARIDA, Caiman (1904). 



Carapace leaving at least four of the thoracic somites distinct ; two 

 movable segments are separated from the anterior part of the head, bear- 

 ing respectively the pedunculate eyes and the antennules ; protopodite of 

 antenna of two segments ; mandible without lacinia mobilis ; posterior 

 thoracic limbs with protopodite of three segments (the relation of the 

 segments of the anterior thoracic limbs to those of the limbs in the other 

 divisions is doubtful) ; an appendix interna on pleopods ; hepatic caeca 

 much ramified ; heart much elongated, extending through thoracic and 

 abdominal regions ; spermatozoa spherical ; development with meta- 

 morphosis, a free-swimming nauplius stage is not certainly known. 



LITERATURE. 

 (General Morphology and Classification of Malacostraca. ) 



1. Boas, J. E. V. Studien iiber die Verwandtschaftsbeziehungen der Mala- 



kostraken. Morphol. Jahrb. viii. pp. 485-579, pis. xxi.-xxiv., 1883. 



2. Caiman, W. T. On the Classification of the Crustacea Malacostraca. Ann. 



Mag. Nat. Hist. (7) xiii. pp. 144-158, 1904. 



3. Claus, C. Neue Beitriige zur Morphologic der Crustaceen. Arb. zool. Inst. 



Wien, vi. pp. 1-108, pis. i.-vii., 1885. 



4. Hansen, H. J. Oversigt over de paa Dijmplma-Togtet indsamlede Krebsdyr. 



Dijmphna-Togtets zool.-bot. Udbytte, pp. 185-286, pis. xx.-xxiv., and 

 Resume, pp. 508-511, 1887. 



