524 CRUSTACEA. 



established principles in nomenclature. For it is giving the old name 

 to far the smaller, instead of the larger and more characteristic part 

 of a genus, an objection which, if not holding against Leach himself, 

 since the genus at the time of its subdivision by him contained but 

 two species, is still, at the present day, seen to be of much weight. 

 It is giving a name which belonged pre-eminently to one of the fresh- 

 water species, the common one of Europe, and which is properly, there- 

 fore, the type of the old genus, to a division of this genus which does 

 not include the typical species ; for Gesner, as long ago as in the 16th 

 century, called the common species of the European streams Astacus 

 fluviatilis, and Linnaeus named it Cancer astacus, both names including 

 the name Astacus, while the marine species, although early named 

 Astacus marinus, was called by Linnaeus, Cancer Gammarus. Besides 

 this, it is introducing much confusion into the science, not only by 

 changing the long-established names of species, but by giving a new 

 use to the name once applied by Kisso to a species of the genus Tel- 

 phusa. There seem, therefore, to be reasons enough for rejecting 

 Leach's names, if it is of no weight that they remained for thirty years 

 unrecognised by British authors. 



ASTACUS LENIUSCULTJS. 



Rostrum tridentatum, dentibus acutis, medio tenuiter elongate. Carapax 

 Icevis, punctulatus, lateraliter pone rostrum utrinque 2-spinosus; 

 areold inter suturas longitudinales posLdorsales latd. Pedes antici 

 compressi, inermes, non tuberculati, manu Icevi, punctulatd, carpo 

 paulo dblongo, intus recto, inermi, apice interno acuto excepte, brachio 

 antice denticulate, apice interno elongate acute, dor so unispinoso. 

 Pedes sequentes nudiusculi. Segmentum caudale parce oblongum, late- 

 ribus fere parallelis. Pedes 5ti branchias parvas gerentes. 



Beak tridentate, teeth acute, middle tooth slender elongate. Carapax 

 smooth punctulate, behind beak either side with two spines (the 

 posterior obsolescent in young individuals) ; postero-dorsal areolet 

 between the longitudinal sutures broad. Anterior feet compressed, 

 in no part tuberculate or spinous, hand smooth, punctulate ; carpus 



