some British Fossil Crustacea. 



furrow strong, slightly arched backwards, the ends reaching 

 each side margin at a point deeply notched by the abrupt nar- 

 rowing of the margin from thence to the front ; branchial fur- 

 rows double, inclosing between them a narrow, pointed ridge on 

 each side, which meets its opposite fellow at less than a right 

 angle (each meets the midline of the back at an angle of about 

 40°) on a point of the back about halfway between the nuchal 

 furrow and the posterior margin ; abdomen (including the tail- 

 fins) shorter than the carapace, segments very weak, slightly 

 arched, their ends triangularly pointed (ends of the second one 

 not dilated), sixth longer than the preceding ones, giving origin 

 to the two broad, rotundato-trigonal pair of side-flaps of the tail, 

 which are very large, thin, and undivided by transverse sutures ; 

 seventh segment (or middle tail-flap) subtrigonal, thicker than 

 the others and tuberculated ; surface of carapace, legs and 

 chelae covered with large spinose tubercles and intervening 

 granules of very irregular size ; first pair of feet or chela very 

 large, subcompressed, fingers slender, with a row of large 

 teeth on the inner edge, carpus very short, tumid, trigonal; 

 three next pair of legs slender, compressed (? apparently ter- 

 minated by a blunt, trigonal, simple claw) ; fifth pair not 

 seen. 



In the large, flattened, strongly toothed rostrum, rough spi- 

 nose legs, the small size of the abdomen, with the general form of 

 its little-arched, weak segments, and the undivided outer pair of 

 tail laminae, this genus approaches the recent Galathcea more than 

 any other recent group, differing in its peculiar branchial fur- 

 rows and ridges, meeting at an angle on the middle of the back, 

 &c. The long, dentated rostrum, large, rough, spinose tubercu- 

 lation of the carapace and chelae easily distinguish those large cre- 

 taceous species from the diminutive genera Clytia and Glyphcea 

 of the oolitic rocks with which they have been hitherto con- 

 founded. The type of the genus is the Astacus Leachii (Mant.), 

 to which at least the figures marked f. 1 & 4. t. 29 of the ' Geo- 

 logy of Sussex ' refer (some of the other figures possibly belonging 

 to the E. brevimana, M'Coy). The E. Leachii is also well figured 

 and described by Reuss in his f Versteinerungen der bohm. 

 Kreideformation/ and by Geinitz in his ' Char, der Schich. u. 

 Pet. des sachsisch-bohmischen Kreidegebirges/ It is distin- 

 guished by the very long, straight, narrow fingers of the chelae, 

 which are nearly twice the length of the basal part of the hand, 

 or from their base to the carpus, and set on their inner edge 

 with a row of narrow cylindrical teeth their own length apart ; 

 the whole hand (or penultimate joint and moveable finger) 

 nearly one-fourth longer than the carapace. A second species 

 of large size and remarkable form occurs in the chalk of Burwell 



