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sixth abdominal ring is the telson, with a transverse fold in the 
middle; and, beneath the telson on each side are two broad 
plates, the highly modified swimmerets of the sixth ring. This 
structure—the telson in the middle with the two plates on each 
side—constitute the flapper of the Cray-fish, by the aid of 
which it executes its retrograde swimming movements. 
The fossil Crustacea, which closely resemble our Cray-fish, 
were first separated from the fresh water genus Astacus in 1835, 
by H. Von Meyer, into the genus Glyphea, erected by him for 
the marine fossil forms of Astacina. In 1840 the same author 
proposed the genus Hryma, for a “ neue gattung foss. Krebse ; ” 
and the genus Clytia for another new form; and the genus 
Bolina Minster for a form allied to Glyphea. Glyphea has 
great affinities with Astacus, from which it is distinguished by 
having the cephalothorax divided into three regions by well- 
marked transverse lines. The first pair of feet also, instead of 
terminating in stout didactyle chele nearly equal in strength, 
have the upper chele formed like a bent claw, and the under 
absent or rudimentary. They are found in the Lias and other 
Jurassic strata. 
Eryma, like Glyphea, has a large cephalothorax, divided by 
well-marked lines into three regions, the middle being prolonged 
much backwards. The anterior pair of feet are shorter, and 
much resemble those of Astacus, and like the forceps of our 
Cray-fish, terminate in a pair of nearly equal-sized chele, and 
by this character alone are they distinguished from Gilyphea, a 
circumstance which renders it impossible to determine to which 
genus a cephalothorax belongs, unless it happens to be associated 
with the anterior feet or forceps of the animal. 
The fossil which I have the pleasure of introducing to the 
notice of the members of the Cotteswold Club, was obtained 
from the Fimbria marl of Leckhampton hill, out of the mud- 
stone derived from the middle coral reef of the Inferior Oolite, 
in the zone of Harpoceras Murchisone. 
Astacomorphous Crustacea are very rare in our Oolitic rocks, 
but the well-marked cephalothorax figured above places the fact 
beyond dispute. I am inclined to place this fossil in the genus 
