Yol. 54.] THE DECAPOD CETJSTACEA. OF ENGLAITD. 17 



distinct carinse, which border the rostrum on each side, extend 

 backward and outward, and bound a space which anteriorly and 

 laterally encloses the mid-gastric lobes ; a central ridge runs along 

 the dorsal groove of the rostrum and the mesogastric lobe, and 

 bifurcates midway towards the cervical sulcus. Between the mid- 

 gastric lobes and the antero-lateral margin occurs another indistinct 

 ridge, which terminates as a slight blunt process on the frontal 

 border. A narrow, sinuous, cervical sulcus crosses the dorsum 

 about midway between the frontal and the posterior border, and 

 extends obliquely forward to the antero-lateral border. On the 

 scapular region a median ridge commences at the cervical sulcus^ 

 becomes gradually wider and more elevated, and ends as a distinct, 

 blunt process near the posterior border of the carapace. Branchial 

 lobes indistinctly defined ; surface minutely punctate. A rather 

 wide, shallow sulcus apparently indicates the separation of the 

 metabranchial from the anterior branchial lobes. An elevated ridge 

 subtends the posterior and lateral margin of the carapace. 



Abdomen seven -jointed, as long as the carapace; segments of 

 nearly equal length, slightly increasing in width from the first to 

 the fifth ; mesotergal portion of each segment large, slightly 

 punctated, and sparsely granulated near the epimera. Epimera 

 broadly rounded, slightly granulated, marked off from the meso- 

 tergal portion by a ridge. Caudal appendages largely developed. 

 Telson with distinct lateral ridges, and gradually widening towards 

 the posterior border, which is slightly rounded. Endopodite and 

 exopodite respectively equal to the telson in width ; strongly ridged 

 centrally. 



First pair of limbs monodactylous ; the meropodite has a row of 

 acute tubercles on the outer border ; carpopodite subterete, nearly 

 half as long as the propodite. Propodite rather more than half the 

 length of the carapace; surface granulated. Eixed finger rudi- 

 mentary. Dactylopodite slender, half as long as the propodite, its 

 inner border trenchant. 



Specimens vary in length from 13 to 20 mm. 



Remarlcs. — The long slender abdomen, the largely-developed 

 caudal appendages, and the conformation of the chelae are so similar 

 to those of Gebia that I provisionally refer this species to that 

 genus. 



Specimens of this species usually occur in the form of casts, the 

 most characteristic feature of which is the sharply-defined shield- 

 shaped dorsal lobe occupying the mid-gastric region ; this character 

 has suggested the specific name. Examples in which portions of 

 the test are preserved show that the surface of the cephalic region 

 is granulated, and that the elevations which occur as sharp carinas 

 in the cast are indicated by corresponding, but broader, ridges 

 bearing granules of a larger size than those on the rest of the 

 carapace. Eleven specimens have been examined. 



Distribution. — Great Oolite of Northampton ; in the Woodwardian_ 

 Museum, the collection of Mr. T. J. George, of Northampton, and 

 in my own cabinet. 



Q. J. G. S. No. 213. c 



