108 On the Jstacilla of Cordiner, 



however, never probably examined the work; as Dr. Leach 

 having, by mistake, in quoting the "Miscellany," under the 

 species just referred to, named the twenly-first plate instead 

 of the twenty-third^ and this typographical error has been 

 transferred to the pages of Desmarest. 



In the thirteenth volume of the Edinburgh Philosophical 

 Journal^ conducted by Professor Jameson (for October 1825), 

 the Astacilla of Cordiner was produced a second time, by Dr. 

 Johnston, of Berwick, not only as a new species, but as con- 

 stituting a new genus, under the title Leacia lacertosa. This 

 zealous observer perceived, as Cordiner had previously done, 

 that, in its characters, this crustaceous animal differed from 

 all the genera which had been previously instituted ; though 

 he considered it as associating best with the Asellides of 

 Lamarck, a group which includes the genera Asellus, Idotea, 

 Sphoeroma, Cymothoa, and Bopyrus. The name of the genus 

 was intended as a compliment to my valued friend, Dr. Leach, 

 ^nd the following character was assigned to it. " Antennae, 

 four ; the superior very short ; the inferior nearly as long as 

 the body. Body linear, of nine segments; the four first, and 

 the four last, short, transverse, and brading appendages ; the 

 mid one naked, half the length of the body. Legs of two 

 kinds ; those attached to the anterior segments, formed for 

 swimming, and those to the posterior, for creeping. Caudal 

 segment mucronate, with two lamellae beneath, inclosing di- 

 vided styles." 



Had this generic character been accurate in all the par- 

 ticulars of which it consists, a very useful addition would 

 thereby have been made to the systematical arrangement 

 of crustaceous animals. But, unfortunately, the mistakes 

 which have been committed in its construction are of such 

 a kind as to destroy its value, and to excite a regret that, 

 amidst several successful efforts at minute description, there 

 should occur any room for censure. 



The body of the animal, exclusive of the head and the tail, 

 consists not of nine, but of seven segments, the ordinary 

 number of its congeners. The middle segment of the body, 

 or the fourth, instead of being naked, or, as it is stated in the 

 description, ** resembling in form the middle shield of the 

 lobster tribe, but peculiar in having affixed to it neither feet 



