B. W. Eooky—A New Wealden Turhise. 265 



The vertebral shields are wider than long, the first by If laches, 

 the second and third by 1 inch, the fourth by ^ inch. The area 

 ■underlying the second and third vertebral shields is slightly fluted, 

 that under the others is smooth. 



The entoplastral is wide, and rounded anteriorly and posteriorly ; 

 mesoplastrals are absent. The suture between the hypo- and the 

 xiphiplastrals commences below the apex of the sulcus dividing the 

 anal and femoral shields, thence it ascends and terminates nearly at 

 the top of the inguinal notch. The sulcus dividing the abdominal 

 ■and femoral shields is entirely on the hypoplastrals ; it ascends 

 towards the hyoplastrals, and terminates in the inguinal notch. 

 The anal shields extend on to the hypoplastrals. The total length 

 of the plastron is 12i inches. 



From the above particulars I conclude that the specimen belongs 

 to the genus Flesiochehjs (Riitimeyer). It differs from P. valdensis 

 by the very slight fluting of the area underlying the vertebral 

 shields ; indeed, as mentioned, this is absent except under the second 

 and third. It can be distinguished also by the fact that the vertebral 

 shields extend only one-third across the costal bones ; in this respect 

 it agrees with P. Brodiei. The shape of the shields differs from that 

 seen either in /'. Brodiei or P. valdensis, and approaches very nearly 

 to the form characteristic of Pleiiro sternum concinnum. The shape of 

 the nuchal bone is different from that of the other species mentioned, 

 and the entoplastral, instead of being V-shaped posteriorly, is rounded. 

 The suture of the xiphiplastral bone in P. Brodiei is very nearly 

 horizontal, whilst in the specimen now described it ascends and 

 terminates a little below the inguinal notch. 



I endeavoured by the matrix, the Pnludinn seam, and Cyprids on 

 the surface of the carapace to fix the exact horizon whence the 

 specimen came, but after diligent and careful search could not locate 

 closer than it is within the 49 feet of Wealden shales immediately 

 overlying the sandstone of Cowlease Chine and Barnes High, there- 

 fore about 120 feet more or less below the Perna Bed ; but if the 

 Cyprids on the carapace prove to be Candona Mantelli (Jones) this 

 would, I think, be sufficient to fix the horizon at 100 feet below the 

 Perna Bed in the 9 feet of shales with Candona 3Iante}li (Jones) in 

 the section on p. 15, Memoirs of Geological Survey, Isle of 

 Wight, 1889. 



My amateur examination seems to point to this being a new 



species; if it be so I would suggest Plesiochehjs vectensis as its name. 



Explanation of Page-plate Illustration (p. 264 opposite). 



Fig. 1, A. — The carapace (dorsal aspect). 



Fig. 2, B. — The plastron (ventral aspect). 



ab. Abdominal shields. hnin. Humeral shield. 



an. Anal shields. hpp. Hypoplastral plate. 



c 1-8. Costal plates. ht/p. Hyoplastral plate. 



cs 1-4. Costal scutes. i(/. Intergular plate. 



entp. Entoplastral plate. n 1-8. Neural plates. 



ep. Epiplastral plate. nu. Nuchal plate. 



fem. Femoral shield. xp. Xiphiplastral plate. 



ff. Gular shield. v 1-4. Vertebral shields. 



M= matrix. 



