48 J. R. KiNAUAN on the Britannic Species of 



nuto in medio arniata ; dcntibus v. spinis kteralibus nullis. Pedum primi 

 paris palma obliqua, fere longitudinalis. Pedes quinti eos primi paris superan- 

 tes. Abdomen vis carinatum ; cauda valde compressa. Long. 0.9 poll. 

 Prod. 93. 



(6). Crangon carinicauda (Stimpson). — Curapax depressus, pubescens, 

 septcmcarinatus ; carinis la^vibus, retrorsum distinctis ; mediana antice obso- 

 lete ; tribus lateralibus approximatis. Eostrum valde angustatum, longitudi- 

 ualiter sulcatum extremitate bifidum. Abdomen insculptum, sulcis plerisque 

 transversis, pubescentibus ; segmentis tertio quarto quintoque gibbosis, valde 

 carinatis. Long. 0.66 poll. Prodromus 93. I have abbreviated some of these 

 descriptioiis. 



Before entering into the details of the Britannic species, it will be proper to 

 consider vjrhether at least three genera are not distinguishable ; to the better 

 understanding of which question, it will be necessary to set forth the views 

 adopted in this paper as to the homologies of the family type. 



ON THE GENERAL nOlIOLOGIES. 



Adopting the view which recognizes the body of the crustacean as normally 

 consisting of twenty-one articulated rings, or somites, distributed as follows : — 

 (1). Fourteen somites devoted to the appendages of special sense, organs of 

 prehension, mastication, respiration, and ambulation, and constituting acephalo- 

 t/iorax (Plate 1. KO) ; (2). Seven somites devoted to the support of natatory 

 and ovigessary appendages, occasionally bearing organs of respiration, and con- 

 stituting the abdomen (Plate I. A) ; we find tliat the following general type 

 plan may be traced : — 



When present, the appendages are (vide Plate I. 1, 2, 3, &c.) — 



1st somite — Eyes and ocular appendages. 



2nd somite — Auditory, or internal antennae. 



3rd somite — Olfactory, or external antennas. 

 . 4th somite — Mandibles. 



5th to 9th — Prehensile organs of mouth, and masticatory organs, viz., max- 

 illa;, or jaws, and maxillipeds — these latter sometimes becoming prehensile, and 

 taking on the office of chelipeds, at least in part. 



