THYSANOPODA COUCHII. 347 



observed to exist in a single case of the numbers I have 

 examined of our present species. Judging from the figures 

 in Dr. Edwards's plates, the carapace in the present species 

 is smaller and more cylindrical ; the cleft in the lower lip 

 is more hollowed, the palp of the thoracic feet is less 

 developed, the abdominal false feet are shorter, and very 

 differently formed ; the middle lamina of the tail also 

 presents some difference in the relative length of the middle 

 and lateral points of its tricuspid apex. One of the most 

 interesting circumstances in the organization of this species 

 is the form of the ovisacs, which, instead of being mere 

 pouches closely adherent to the thorax, are dependent from 

 their attachment by a distinct peduncle. This structure 

 was unknown until I detected it in a single individual, the 

 only female amongst a large number of specimens sent to 

 me by my friend Mr. Couch, who obtained them on the 

 Cornish coast, from the stomach of a mackerel, which 

 appeared to have been making a feast of this rare and 

 interesting little crustacean. The following account has 

 been kindly furnished to me by that gentleman, and shews 

 that it can scarcely be considered as an ordinary inhabi- 

 tant of our coasts. " The mackerel from which the curious 

 shrimps Thysanopoda were taken, were caught almost at 

 mid-channel, or almost ten leagues from us ; perhaps seven 

 or eight south of the Lizard ; and I have not seen any 

 since, although I am much in the habit of searching the 

 stomachs of mackerel and other fishes. There were my- 

 riads in the stomachs of the mackerel at the time when I 

 obtained those which I sent you." I have dedicated the 

 species to that indefatigable and acute observer, to whom 

 we are indebted for so many valuable contributions to 

 natural science. 



The following is a description of the details of the wood- 



