532 Dr. H. Woodward — On a New Fossil Isopod. 



(uropodites), beneath which the outer lobe is generally concealed. 

 Traces of these, and of tbe walking appendages of the thorax, can, 

 unfortunately, only be made out in sections in the matrix. The 

 surface of the head-shield and segments, as far as it has been 

 preserved, is curiously carunculated, and the thoracic segments are 

 also ornamented with lines of small tubercles varying in size ; save 

 the large spines and prominences which ornament the abdomen and 

 telson, we are unable to speak on account of these portions having 

 been decorticated ; but we may fairly conclude that the surface was 

 carunculated like the head-shield. There is a tendency towards 

 a median line of small tubercles down the dorsum, commencing with 

 a rather prominent one in the centre on the posterior border of the 

 cephalon. 



Dimensions. — Greatest breadth of cephalon, 25 millimetres ; length 

 13 mm.; greatest breadth of thorax 33 mm.; length of seven 

 thoracic segments on median line 13 mm. ; length of abdomen and 

 telson united 15 mm. Total length of fossil 41 mm. 



Formation. — Great Oolite. Locality. — Northampton. 



In the cabinet of Thomas Jesson, Esq., B.A., F.G.S. 



Observations. — This is certainly one of the most curious examples 

 of fossil Isopods I have yet seen. Its remarkably-shaped cephalon 

 recalls to mind the genus Lichas amongst the Trilobites, but the 

 general form is that of a true Isopod ; nevertheless there are several 

 points of great interest in the fossil before us. Besides the trilobation 

 of the head-shield, one cannot fail to notice the prominent marginal 

 eyes inclosed by the first thoracic somite, as is the case in the living 

 genus Sphceroma. This segment, in Spheeroma ; and the first and 

 second thoracic segments united to the head in Serolis (see foot- 

 note p. 530), are no doubt homologous with the genal portion (or 

 " free-cheek " of Salter) in the head-shield of the Trilobites, thus 

 affording another link by which to connect the modern Isopoda with 

 the ancient and extinct Trilobita. 1 



I know of only one living form among the Sphceromidce. having 

 such strong ornamentation upon the segments, head-shield and 

 telson as is seen in Oyclosphceroma ; I allude to the curious little 

 form obtained by Dr. Milligan, at Flinder's Island, Bass's Straits, 

 and named by the late Adam White Ceratocephalus Grayanus, MS. 2 

 (see PI. XV. Figs. 2a, b, c). It has three horn-like prominences 

 on its head-shield, and the telson has the same prolonged pointed 

 termination as in our fossil, with similar protuberances and rugosities 

 on its abdominal shield. 



From Archwoniscus (PI. XV. Fig. 4) the only other British Isopod 

 from the Oolitic Series. Cyclospliceroma entirely differs, that Purbeck 

 genus being now referred to the Mqidce 3 on account of its free 

 abdominal segments. 



1 See remarks in Monograph on the British Carboniferous Trilobites, by H. 

 Woodward, Pal. Soc. Mon. 1883-84. p. 76. 



2 See Article "Crustacea," Encyclopajdia Britannica, 1877, ninth edition, vol. vi. 

 p. 659, fig. 72, a-e, by H. Woodward. 



3 See my paper " On Eocene Crustacea from Gurnet Bay, Isle of Wight," Quart. 

 Jouru. Geol. Soc. 1879, vol. xxxv. pi. xv. pp. 342-350, on Archceoniscus, p. 349. 



