Classification of the Crustacea Malacostraca. 157 



pair of movable articulated rami (caudal furca). An adductor 

 muscle runs transversely between the two valves of the 

 carapace. Thoracic limbs all similar, more or less foliaceous, 

 with protopodite of three segments. 



Series EuMALACOSTKACA. — Abdomen of six somites 

 (the number may be reduced by coalescence), the last of 

 which typically bears a pair of appendages, and a telson 

 which never bears movable furcal rami *. No adductor 

 muscle of the carapace. Thoracic limbs rarely all similar 

 (Eupliausiacea), typically pediform ; protopodite of two seg- 

 ments, except in Stomatopoda. 



Division Syncarida. — Carapace absent. All the thoracic 

 somites distinct. Eyes pedunculate. Antennal protopodite 

 of two segments. Mandible without lacinia mobilis. 

 Thoracic limbs flexed between fifth and sixth segments. No 

 oostegites. No appendix interna on pleopods. Hepatic 

 ca?ca numerous. Heart much elongated, tubular. 



Division PerACARIDA.— Carapace, when present, leaving 

 at least four of the thoracic somites distinct. First thoracic 

 somite always fused with the head. Antennal protopodite 

 typically of three segments. Mandible with lacinia mobilis 

 (except in parasitic and other modified forms). Thoracic 

 limbs flexed between fifth and sixth segments. Oostegites 

 attached to some or all of the thoracic limbs in female, form- 

 ing a brood-pouch. No appendix interna on pleopods. 

 Hepatic cajca few and simple. Heart elongated, extending 

 through the greater part of thoracic region, or displaced into 

 abdomen. Spermatozoa filiform. Development taking place 

 within the brood-pouch ; young set free at a late stage. 



Division EuCARlDA. — Carapace coalescing dorsally with 

 all the thoracic somites. Eyes pedunculate. Antennal 

 protopodite with, at most, two distinct segments. Mandible 

 without lacinia mobilis in adult. Thoracic limbs flexed 

 between fourth and fifth segments. No oostegites. An 

 appendix interna sometimes present on pleopods. Hepatic 

 cseca much ramified. Heart abbreviated, thoracic. Sperma- 

 tozoa spherical or vesicular, often with radiating appendages. 

 Development as a rule with metamorphosis. A free-swimming 

 nauplius-stage in the more primitive forms. 



* The movable appendages of the telson in Eupliausiacea are modified 

 setee (Sars, 'Challenger' Kep., Schizopoda, p. 162). 



