52 THE ENTOMOSTRACA OF 



in a new sub-genus, Cytherideis (see p. 46) ; for instance, C. anyusta, ' Monog. Cret. 

 Entom.'pl. 6, fig. 18. 



Amongst the " Bairdiae" of Bosquet, Reuss, and Bornemann, there are, I believe, 

 included several species both of Cytheridea and Cytherideis. 



No. 1. Bairdia subdeltoidea, Miinster, sp. Plate IV, figs. 2 a, 2 b, 3 ; PI. VI, 



figs. 1 a, 1 b, 2. 



Cythere subdeltoidea, Miinster. Jahrb. f. Min., &c, 1830, p. 64; Neues Jahrb. f. 



Min., &c, 1835, p. 446. 

 Cytherina subdeltoidea, F. A. Roemer. Ibid., 1838, p. 517, t. 6, fig. 16. 



— — Hauer. Ibid., 1839, p. 429. 



— — F. A. Roemer. Verstein. Nordd. Kreid., p. 105, t. 16, fig. 22. 



— — Geinitz. Charact. Sachs. -Bohm. Kreid., 3 Abth., p. 64. 



— — lb. Grund. Verstein., p. 244, t. 8, fig. 21. 



— — Reuss. Verstein. Bohm. Kreid., 1 Abth., p. 16, t. 5, fig. 38 ; 



and 2 Abth., p. 104. 



— — lb. Haidinger's Abhandl., iii, p. 49, t. 8, fig. 1. 



— — lb. Ibid., iv, p. 47. 



— — lb. Apud Geinitz, Quadersandst. oder Kreid. Deutsch, p. 98, 



No. 10. 



— — Eichwald. Lethaea Rossica, t. 11, fig. 23. 



— — Naumann. Lehrb. Geogn., 2. Hjilfte, t. 60, fig. 24. 



— trigona, Bosquet. Mem. Soc. Roy. Liege, iv, p. 358, t. 1, fig. 3. 

 Bairdia subdeltoidea, lb. Mem. Couron. Acad. Belg., xxiv, p. 29, t. 1, fig. 13. 

 Cythere (Bairdia) subdeltoidea, Jones. Monog. Entom. Cret., p. 23, t. 5, fig. 15. 



— — — Reuss. Denkschrif't. d. Akad. Wiss. Wien., vii, pp. 41, 



139. 



INCH. 



Length, J T J ff T ^ Recent : Britain ; West Indies ; Mauritius ; Manilla ; Australia. 



Tertiary : Britain ; Europe ; Virginia. 

 Cretaceous : Britain ; Europe. 



Carapace triangular, gibbous, acute at the extremities, smooth or setiferous and 

 sometimes finely punctate ; right valve smaller and more angular than the left. [For 

 a fuller description of the valves, see ' Monog. Entom. Cret. Form.,' p. 23.J 



Cythere {Bairdia) subdeltoidea is a common form in the Tertiary deposits throughout 

 Europe ; it is plentiful in the Tropical Seas, 1 and occurs also on the British coasts. 2 



1 The B. subdeltoidea of Australia is punctate, and has the rosette-like lucid spots of the Chalk form 

 of this species ; that of Turk's Island, Bahamas, more resembles the Crag form both in its globosity and in 

 the less compactness of the spots. 



'-' The B. subdeltoidea of Arran, here referred to, is evidently a variety, being narrow and presenting a 

 difference in the arrangement of its lucid spots. 



