Miscellanea Zoolugica. 369 



turalists to classify them in one and the same genus, and it is suf- 

 ficiently close to justify us in calling them Sea-spiders, were an En- 

 glish name necessary for their identification. They are characte- 

 rized by having a crustaceous slender body, not much thicker than 

 the limbs, and which may aptly enough be compared to a short 

 vertebral column, each segment representing a vertebra with its 

 prominent lateral processes. This column is divided into five seg- 

 ments only, which are so far anchylosed that their joints appear to 

 admit of no motion upon one another, either to a side or perpendicu- 

 larly : the anterior is rather the largest, and on its vertex there is 

 a tubercle or small wart surmounted by four simple eyes placed in 

 a square, but which are very difficult to detect in some of the spe- 

 cies, if they are not actually wanting. I believe that this anterior 

 segment is formed by the confluence of two — a cranial and thoracic, 

 and in the Pycnogonum, the evidence of this division may be faint- 

 ly traced. The cranial portion is sometimes lengthened out into the 

 form of a neck and head, terminated with a short proboscis, but in 

 others the proboscis springs directly from the truncate front into 

 which it is inserted as in a socket. It is a tubular organ, of a crus- 

 taceous texture, of extremely limited motion in a vertical direction, 

 and with a simple round or trifid aperture at its apex, but in most 

 of the genera the inferior side is divided into two equal halves by 

 a longitudinal line or plain suture. * Generally at the base of this 

 proboscis we find a pair of mandibles formed of two joints, the ulti- 

 mate armed with a pair of claws or pincers, one of the claws only 

 moveable ; and in one genus there is in addition to these a pair of 

 filiform articulated organs, which have been named the palpi. All 

 these belong to the cranial segment, if it is allowable to speak of 

 this as distinct. The thorax consists of four segments, including the 

 cranio-thoracic ; and each of them supports a single pair of legs, 

 articulated with the protuberant sides of the segments. The legs 

 are all alike in form, and calculated solely for creeping; they are 

 eight-jointed, t and the tarsus is provided with one or two strong 



* Savigny says that in the terminal mouth we can scarcely perceive some 

 traces of a lip and jaws, — and the manner in which the sentence is worded in- 

 duces the belief that he could not discover any. Mem. sur les Anim. sans Vert. 

 i. 55. The proboscis of a large species of Phoxichilus, from the Cape of 

 Good Hope, appeared to be composed, says Latreille, of a lip, of a tonguelet, and 

 of two jaws, the whole soldered together. Hence the palpi belong to the jaws, 

 — Cuvier, Reg. Anim. iv. 276. 



f The three basal joints constitute the coxce, the next the thigh, the two fol- 

 lowing the tibia, the other two the tarsus, but this nomenclature is objection- 

 able in as far as it is founded on some very doubtful analogies between the parts 

 so named, and the corresponding parts of vertebrate animals. 



