Crustacea. 5617 



harbour crab (Carcinus 3Ianas) of the same dimensions : when fatigued, therefore, it 

 descended to the bottom ; but I conclude it will readily use any floating substance to 

 relieve its swimming powers and prevent the necessity of sinking, for when a stone 

 was placed in the tank it mounted to where it nearly touched the surface, and when 

 the shannies (Pholes) in the tank attempted to get on it, the crab repeatedly drove 

 them away : it was, however, quite alive to the danger of its position, and when it 

 perceived itself observed, presently left its lofty rock. For a considerable time the 

 sea-water in which this crab was preserved maintained its sweetness without taint, — 

 longer, it was supposed, than under ordinary circumstances ; but the presence of a 

 dead fish was fatal ia a very few hours. — Jonathan Couch ; Polperro. 



Description of a new British Species of Shrimp. — This hitherto undescribed 

 species of Crangon is clearly allied to the common shrimp (C. vulgaris, Fab.), differing 

 in one or two well marked characters, as the following description shows: — 



Ceangon Allmanni. 



Specific characters: — Carapace smooth, armed with three spines, one on the 

 median gastric region and one on each branchial region ; the sixth segment of the 

 abdomen is deeply channelled above through a well-marked carina which borders it 

 on each side ; the seventh segment is also channelled. The anterior pair of legs are 

 moderate in length, the arm smooth, and entirely free from spine or tooth ; the second 

 pair of legs are slender, and slightly longer than the third ; the external footgerms are 

 similar to those of C. vulgaris, but their superior articulation slightly more elongated; 

 the rostrum is triangular and longer in proportion than in C. vulgaris. The sternal 

 spine is very short in the males and altogether absent in the females ; each segment of 

 the abdomen is, however, armed with a short spine between the origin of abdominal 

 false feet. The external antennae, the antennal scales, the external natatory plates of 

 the tail all resemble C. vulgaris ; the middle plate is more acuminate than in that 

 species, and armed^with twelve teeth, viz. four lateral, two inferior terminal, and six 

 terminal. The length of my specimens vary from 0*5 inch to 3 inches. Colour 

 bluish gray, with golden, black and red dots scattered through it. 



The most obvious characters which distinguish this from all described species are the 

 sulcate, sixth and seventh segments of the abdomen, the smooth arm and the three- 

 spined carapace: it is an interesting species, as containing the characters of two 

 distinct types, viz. C. sculptus and C. vulgaris. It has occurred to me first in 

 December, 1856, in fishermen's boats along with C. sculptus, C. vulgaris, Hippolyte 

 Cranchii, H. Thompsoni, H. varians, and some of the lesser Paguridce ; on a 

 subsequent occasion, in February, I dredged a female loaded with ova in twenty-five 

 fathoms off the coast of Wicklow. Tt appears to be a plentiful species: six specimens 

 occurred in the first instance. The species must be local, as it is too remarkable in 

 its appearance to have been lightly passed over if observed elsewhere. In selecting 

 a specific name for it, I have taken that of an Irish naturalist, to whose labours, 

 in every branch of Zoology, Irish Natural History is indebted for many and valuable 

 additions, George James Allman, M.D., Professor of Natural History, Edinburgh. — ■ 

 John Robert Kinahan ; Donnybrook, Dublin, March, 1857. 



XV, 2 N 



