REPORT ON THE CRUSTACEA MACRUKA. 199 



that is abruptly smaller than the terminal joint of the peduncle, is slightly compressed, 

 and is subequal in length to the carapace. 



The ventral portion of the second antennal somite forms the metope ami passes laterally 

 beneath the frontal margin of the carapace, with which it is closely connected by 

 membranous if not calcified attachments. The anterior portion is produced forwards as 

 a projecting rostrum and sends a keel-shaped process up between the peduncles of the. 

 second paii- of antenna} as far as the distal extremity of the third joints. It is generally 

 furred with short hairs and armed on each side with four or five small tooth-like processes. 



The lower margin is developed into a transverse bardike epistoma, at the extremities 

 of which is a cupdike hollow that receives the anterior articulating process of the 

 mandibles. 



The mandibles (d) are broad concavo-convex appendages, the convex surface from the 

 extremity of the incisive margin to the distal articulating extremity of the apophysis is 

 external, while the concave surface from the same articulation to the transverse molar 

 ridge is internal. The mandible thus forms the inner wall of the channel of exit from 

 the branchial chamber, and forms a partition between it and the internal viscera. The 

 psalistoma has the margin rounded and armed with three cusps, of which the centre is 

 the largest, and indications of others exist along the posterior margin, while the molar 

 ridge is produced anteriorly as a long process, the extremity of which articulates in the 

 cup at the lateral extremity of the epistoma ; between this articulation and the base of 

 the psalistoma articulates a three- jointed synaphipod which is short, hairy, and curved so 

 as to correspond with and fall into the concave surface between the psalistoma and the 

 molar ridge, which it occupies jointly with the lateral processes of the styloglossa. The 

 articulation at the extremity of the apophysis is cup-shaped, and rolls upon a rounded 

 tubercle that projects from the inner surface or ridge that corresponds with the cervical 

 fossa upon the external surface of the carapace. 



The first pair of siagnopoda (e) is three-branched, the inner ramus is short, rigid, and 

 curved ; the central is broad, flat and truncate, and the outer is cylindrical, slender, and 

 biarticulate. 



The second pair of siagnopoda (f) is three-branched and four-jointed; the first or coxal 

 joint is short and supports a large mastigobranchial plate that posteriorly reaches into 

 the branchial chamber and anteriorly sweeps the channel of exit ; the second or basisal 

 joint is of considerable tenuity and divided into two foliaceous branches ; the third joint is 

 similar to the second, but broader and more leaf-like; the fourth joint is long, slender, and 

 tapering, and reaches beyond the anterior extremity of the mastigobrauchia, but not as 

 far as the distal extremity of the preceding branch. 



The third pair of siagnopoda (f) is drawn of the natural size and therefore 

 appears comparatively much smaller than the second, which is drawn two and 

 a half times larger than its natural size. It consists of four joints that are obscurely 



