278 PROF. p. M. dttkcan's eevision op the 



The tubercles are rery unequal, some being much larger than 

 others, and few and far between. 



Fossil. Miocene: Europe. 



It is stated in the description of the solitary species that the 

 plastron is slightly hollowed out around the peristome, which has 

 a very projecting lip. The ambulacra are indistinct, and it 

 appears from the figures that they are flush with the test and not 

 petaloid. 



De Loriol places the form near Argopatagus, A. Agass., but 

 notices that he cannot state anything about the presence of 

 fascioles. 



The combination of the peculiar ambulacra and the pair of close, 

 probably disunited, generative plates (basals) with a projecting 

 lip are dwelt upon by the careful naturalist to whom we owe 

 the genus. 



III. Family LESKiiDiE, G-ray. 



Test thin, ovoid. Apical system with three basal plates fused 

 into one, two large genital pores only and upon conical promi- 

 nences. Peristome excentric in front, pentagonal, with five 

 angular buccal plates. Periproct circular, and with from five to 

 seven plates. A peripetalous fasciole. 



Genus Palceostoma. 



Grray founded the genus Leslcia in 1851, the name being 

 already employed in Natural History. Subsequently Loven in 

 1867 diagnosed the genus Palceostoma, which is identical with 

 Leshia. Grray distinguished the generic characters. 



Genus Pal^ostoma, Loven, 1867, Of vers. Kongl. SvensTc. VetensTc.- 

 Ahad. Forhandl. no. 5, p. 432 ; 1874, Etudes, p. 50, figs. 39, 

 197-199 ; 1883, Pourtalesia, p. 79, pi. xvi. 



Syn. Leshia, Grray, 1851, Ann. & Mag. ISTat. Hist., and 1855, 

 Cat. Eec. Ech. Brit. Mus. pt. i. p. 63. 



Test thin, moderate in size, ovoid, broadest behind the centre 

 and anteriorly, more or less narrow posteriorly, tall and sub- 

 globose abactinally, highest behind, convex actinally, anterior 

 groove slight. 



Apical system subcentral, small, three of the basal plates fused 



