Mr. T. R. Jones on some species of Lepei'ditia. 99 



ings. Nor would the valves, thus ideally constructed, be without 

 considerable resemblance in outline to the Leperditia valves. 

 Moreover, the vertical dorsal sulcus, wliich is scarcely a])parent 

 in the tyjjical Leperdttia, though strongly marked in another 

 section of the grouj), and present also in Beijrichia, would find 

 its homologue in the nuchal furrow of the folded Apodoid. 



Burmeister*, in his review of the classification of the fossil 

 Entomostraca, observed that Hisinger^s two Gothland species 

 (together with Kloden's C. phaseolus) should be regarded as be- 

 longing to a group distinct from the Cytheres. He proposed to 

 retain the generic term Cytherina f for them, and to found on 

 them a distinct family {Cytlierinida:) of the Phyllopuda ; referring 

 to Estheria as a closely allied genus. Keyserliug and Eichwald 

 quote L. Balthica as a " Cypridina." 



There can be little doubt that Leperditia and its allies are suf- 

 ficiently distinct from the known Entomostracan groups to con- 

 stitute a separate family, as Burmeister recommended. The 

 Leperditida (as I propose to term this group), comprising Leper- 

 ditia, Beyrichia, and some other forms not yet described, may be 

 regarded as most probably coming within the pale of the Phyl- 

 lopoda. 



EXPLANATION OF PLATES VL and VIL 



Plate VL 



[The figures (excepting fig. 1 c) represent the specimens magnified two 

 diameters.] 



Fig. 1 . Leperditia Balthica : a, right valve ; h, the same, anterior extremity ; 

 c, the same, central sjjot and anterior tubercle, highly magnified. 

 — From Mr. Morris's Cabinet. 



Fiy. 2. Leperditia Balthica : a, left valve ; b, the same, anterior extremity. 

 [This specimen being somewhat worn, does not well show the 

 sharp angle of the ventral edge.] — From Mr. Morris's Cabinet. 



Fig. 3. Leperditia Balthica : a, perfect carapace, showing the right valve ; 

 b, the same, sho^^•ing the left valve ; c, the same, showing the 

 dorsal aspect ; d, the same, showing the ventral aspect ; e, the 

 same, showing the anterior extremitj. — Mr. Morris's Cabinet. 



Fig. 4. Leperditia Balthica : a, cast of the interior of a left valve, showing 

 the anterior and central tubercles, and the radiating vascular 

 markings ; b, the same, ventral aspect ; c, the same, showing the 

 anterior extremity. The dotted lines represent an ideal section 

 of the carapace. — Museum of the Geological Society. 



Fig. 5. Leperditia Balthica : a, cast of the interior of a left valve of a 



* Organiz. d. Trilob. pp. 57 & 63. (Ray edit. pp. 49 & 55.) 

 t The name " Cytherina " was substituted by Lamarck for Midler's 

 Cythere, and has been used by numerous wTiters in the same sense. 

 Although "Cjthere" has been restored to its original use, and the word 

 " Cytherina " is adrift, still, from the frequent misuse of the latter term, it 

 is not ehgible as a generic appellation. Dana has lately used the tenn 

 " CjrtherinjE " to represent a subfamily. 



7* 



