ANNULOSA : CRUSTACEA. 233 



DIVISIONS OF ClRRIPEDIA. (AFTER DARWIN.) 



ORDER I. THORACICA. 



Carapace, either a capitulum on a pedicle, or an operculated shell with 

 a basis. Body, formed of six thoracic segments, generally furnished with 

 six pairs of limbs ; abdomen rudimentary, but often bearing caudal appen- 

 dages. Mouth, with labrum not capable of independent movements. 

 Larva, firstly one-eyed, with three pairs of legs ; lastly two-eyed, with six 

 pairs of legs. 



Fam. I. Balanida. 



Sessile, without a peduncle ; scuta and terga (forming the operculuni) 

 provided with depressor muscles ; the rest of the valves immovably 

 united together. 

 Fam. 2. Verrucidce. 



Sessile. Shell asymmetrical, with scuta and terga, which are 



movable, but not furnished with a depressor muscle. 

 Fam. 3. Lepadidce. 



Pedunculated. Peduncle flexible, provided with muscles. Scuta 

 and terga, when present, not furnished with a depressor muscle. 

 Other valves, when present, not united into a single immovable 

 case. 



ORDER II. ABDOMINALIA. 



Carapace flask-shaped ; body formed of one cephalic, seven thoracic, 

 and three abdominal segments, the latter bearing three pairs of cirri, but 

 the thoracic segments being without limbs. Mouth, with the labrum 

 greatly produced, and capable of independent movements. Larva, firstly 

 egg-shaped, without external limbs, or an eye ; lastly binocular, without 

 thoracic limbs, but with abdominal appendages. 



Genus. Cryptophialus. 



ORDER III. APODA. 



Carapace, reduced to two separate threads, serving for attachment. 

 Body consisting of one cephalic, seven thoracic, and three abdominal seg- 

 ments, all destitute of cirri. Mouth suctorial. 



Genus. Proteolepas. 



CHAPTER XXXIII. 

 SUB-CLASS ENTOMOSTRACA. 



SUB-CLASS III. ENTOMOSTRACA. The term Entomostraca 

 has been variously employed, and few authorities include 

 exactly the same groups of the Crustacea under this name. 

 By most the division is simply denned as including all those 

 Crustacea in which the segments of the thorax and abdomen, 

 taken together, are more or fewer than fourteen in number 

 the parasitic Epizoa and the Cirripedia being excluded. By 

 Professor Rupert Jones the following definition of the Entomos- 

 traca has been given : 



