98 Dr. H. Woodivard — Fossil Prawns from the Isle of Wight. 



Owing to the presence of orbicular calcite and some iron pyrites 

 in the clay, it is often very difficult to detect the details of the 

 structure of these Crustaceans ; moreover, in order to preserve them 

 from decay, they have to be treated with, a coat of hot gelatine, 

 which, although preservative, is apt to obscure minute details of 

 structure afterwards. 



Pkopal^mon Osbokniensis, H. Woodw. (PI. V, Figs. 1-4.) 



Although there is no one example of the large Osborne shrimp 

 which has been preserved entire, nevertheless, by a careful exami- 

 nation of the fourteen specimens before me, I am enabled to arrive at 

 a fairly correct notion of the separate parts, and so of the prawn as 

 a whole. 



The general outline of its form may be seen from the examples 

 figured on Pi, V, Figs. 1-4, but no restoration has been attempted. 



From Fig. 1 we perceive that the carapace measures 20 milli- 

 metres in length (the rostrum in this specimen is injured and 

 indistinct, but is better seen in Fig. 2) ; the depth of the carapace in 

 profile is 11mm.; the abdomen ('pleonic somites,' Bate) measures 

 28 mm. in length, minus the telson, which, although wanting in 

 Fig. 1, is supplied by Fig. 3, and is 10mm. long; the lateral 

 lobes of the tail-fin being about equal in length, or a trifle longer 

 than the telson. In Fig. 2 the rostrum shows five distinct teeth or 

 serrations ; a single spine is also to be observed on the hepatic 

 region of the carapace in Figs. 2 and 4 ; the bifid flagella of the 

 inner antennse are preserved in Figs. 1 and 2, but the fragmentary 

 remains of the long outer antennae are only imperfectly seen on 

 some of the slabs ; the long slender ambulatory legs measure 25 mm., 

 they are shown in Figs. 2 and 4. But the first and second long 

 and slender chelate limbs are too imperfectly preserved to be made 

 out satisfactorily, though I believe both of them to be present. The 

 abdominal swimming feet (pleopods) are well preserved in Figs. 1 

 and 2, and are about 12 mm. in length. The pedunculated eye can 

 be seen in Fig. 2 and also in Fig. 4. 



In size this prawn closely agrees with the living Palcemon affinis, 

 M. Edw.^ (PI. V, Fig. 8), but the rostrum in the living form is 

 considerably larger and more strongly serrated, both above and 

 below. The segments of the abdomen (pleon) in the fossil form 

 closely resemble the living genus, but the pleopods are perhaps 

 somewhat longer in the Osborne specimen. 



Having regard to the difficulties of dealing strictly with such 

 imperfect material, I venture to define the fossil form as Propalcemon, 

 and for a trivial name I have called it after its locality, Osborniensis. 



Propal^mon minor, H. Woodw. (PI. V, Figs. 5-7.) 

 '?. This little form, of which fifteen examples have been obtained by 

 Mr. Colenutt, from the same beds as have yielded the larger species 

 (P. Osborniensis), measures 26 mm. in length (of which the carapace 

 measures 10 mm., the pleon 11mm., and the telson 5 mm. The 



1 Fiff. 8 is drawn in our Plate of twice the natural size. 



