juNts.J I'AL^EOZOIC OSTRACODA. 75 



PI. xi, fig. 3. Length 4*5 (hinge line 4-3), height 2-7 mm. 



This \H much like Kloodon's " ;ihnost fully grown " type (op. cit., ISiH, 

 pi. i, tig. 21), but the antoi-ior lobe is more com])letely divided in our 

 cast, the middle lobe is isolated, and the hinder lobe is less distinctly 

 j)almate. It is, also, to some extent, like one of Boll's typical figures 

 (18G2, tig. 1 b) ; but the oblique segments of the gigot (hinder) lobe of 

 this internal cast show a moi-e palmate arrangement, and not the quasi- 

 spiral aspect that the outside of the valve usually suggests, ft is like 

 Krause's ''third variety," op. cit., 1877, p. 31, pi. ii, fig. 3, except that 

 the margin and the divided front lobe are not tuberculate, our casts not 

 having retained any evidence of the tubercles. Compare, also, Renter's 

 ^^ tuberc/tlata-(jibbosa,'' op. cit., 1885, j). G34, ])1. xxv, fig. 2 A; this has 

 tubercles on the lobes and margin, and the sausage-lobe is constricted, 

 not divided. The ventral portion of the gigot-lobe in our fig. 3 shows 

 some indication of at least two elevations or tubercles, hence this cast 

 a])pi'oaches still more nearly to B, Bronnl, Reutei*, op. cit., p. (i38, pi. 

 xxv, figs. (I A and (! B, though no evidence of tubercles on the other 

 lobes is visible. In fact the varietal gradations among the above- 

 mentioned forms, and between thera and others, are so numerous and 

 shifting that 1 |)refcr to treat of the cast, fig. 3, as a representative of 

 the typo sufllciently good to bear its name. 



From Stonehouse Brook, Arisaig, Nova Scotia, in dark-grey lime- 

 stone, with luematitic stains, and made up of small organisms, such as 

 the Ostracoda, together with 14 species * of mollusca, brachiopoda, 

 and trilobites, and some oncrinital remains. Upper Silurian (Upper- 

 Ludlow) Formation. Dr. lloneyman's " Arisaig Group f. Division 

 D". ((V)llocted by Mr. Weston.) 



There are also hollow casts of />. tuberculata and some varieties in 

 the sandstone of the same formation at McAdam's Brook, Arisaig. See 

 further on. 



* Detennincil l>.v Mr. H. M. Ami, namely: Miirchisonla Ari.iaigens't\\\ Hall, M. Nova-ficotica, H., 

 \ii('iifittn erecttis', U.. .V. ruiuatn^, H., xV. titthorattta, II., ^^<•ga))lb<)Hi(X crtnrt llata, IL, Pfen'iira, sp., 

 P/io/idopt sQii<ii)>iformi'i,H., Lingnla, sp., lihi/nchonelUx, sp., Chonctfs tcniiistriata, H.. Spir^frra 

 '•nbsulvtta, \ar. peHafn, H.| Crania Acadtensis, H., Cahnnene, sp., Dulmania Logani, H., 

 lif'Un'clna /xrv^iffosfr, H., Convilitvs tie.vuo-wf, II., var. gracilis, II. 



t See Quart. Journ. Geol. Soc. vol. XX, ISiU, pp. 333-345, and vol. XXVI, 1S70, pp. 490-492; also 

 * Aciulian (Joolos.v,' 3nl edit., 187S, pp. 565-570. 



