Mr. T. R. Jones on some species of Leperditia. 97 



Central spot. — There is another point of resemblance between 

 Leperditia and the Limnadid(2, namely the great central spot 

 with its vascular markings (PI. VI. fig. 1 c ; PL VII. fig. 4; d). 

 In Leperditia there appears to be only one circular canal ; in 

 Isaura [Estheria) ci/cladoides there are three (Joly*), as there are 

 also in Lymnetis, as shown by Grubef. These concentric vas- 

 cular impressions on the inside of the carapace are present also 

 in other Entomostraca, as for instance, on the lateral halves of 

 the carapace in ApusX and Lepidurus^. 



The reticulated centre of this spot (which leaves the low warty 

 tubercle on the casts of the fossil valves) is the place of attach- 

 ment for the great adductor muscle of the animal || (Joly, Grube). 



The radiating canals, originating at the central tubercle, are 

 found in Lymnetis (Grube, loc. cit.) as well as in Leperditia. 



The concentric, radiating, and reticulate markings are pro- 

 bably referable to the course of blood-vessels and sinuses. The 

 carapace of many of these little Crustaceans appears to be ex- 

 tremely sanguiferous, and an important adjunct to the usual 

 respiratory organs. 



The central spot of Leperditia and the Limnadidce is repre- 

 sented in the Cypridinina, Cyprince, and Cytherince by a group 

 of variously arranged minute lucid spots, occupying an analogous 

 position on the valve ; and, in the first-named family at least, I 

 believe the lucid spots certainly to mark the place of muscular 

 attachment. 



Eye-spot. — The anterior tubercle may with probability be re- 

 garded as indicating the place of the eye^, — or possibly even as 

 the external part of that organ ; but, excepting some allied 

 palaeozoic forms, there are no other bivalved Entomostracans 

 having the eye indicated by a tubercle on the carapace, and few 

 have the eye placed so high up in the antero-dorsal region. 



In the Cyprince and Cytherince the eye is single (coalesced), 

 and close up to the anterior hinge. Some at least of the Cypri- 

 dining, in which group the eyes are separate and transversely 

 distant one from another, have the eyes lower down in the an- 



* Annal. Sc. Nat. 1842, nouv. ser. vol. xvii. p. 293 &c. pi. 7-9. 



t Bemerkungen iiber die Phyllopoden, &c., von Dr. A. E. Grube ; 

 Archiv fur Naturgeschichte, 1853, p. 109. pi. 7- fig. 22. 



X Baird's Natural History of the British Entomostraca (Ray Soc), 1850. 



§ Baird, Zool. Soc. Illust. Proceed. 1850. Annulosa, pi. 17. 



II This central tubercle in the fossil Entomostraca has been often mis- 

 taken by palaeontologists for an eye-spot. Eichwald {loc. cit. supra) sup- 

 poses it in Leperditia to be the seat of the ovary, and the associated radia- 

 tions to be ovarian vessels : this is quite untenable ; the eggs are found in 

 the postero- dorsal region of the recent bivalved Entomostraca. 



1[ Count Keyserling (loc. cit. supra) describes this tubercle in L. mar- 

 ginata and L. Balthica as the "eye-tubercle." 



Ann. ^ Mag. N. Hist. Ser. 2. Vol. xvii. 7 



