New Brachiopocl from the Kuckers Stage in Estonia. 363 



(2) The muscular platform of the dorsal valve, with an elevated 

 septum and a trifid cardinal process. 



(3) The more or less sub-parallel shell-callosities of the visceral 

 fields in the ventral valve, surrounded by shell-thickenings, which 

 proceed as dividing branches from the septal process. 



(4) The strong dental lamellae of the ventral valve, with attached 

 curved ridges, enclosing the muscle-area and the septal process. 



(5) The surface structure. 



Genotype : Leptestia musculosa, sp. nov. 



Leptestia musculosa, sp. nov. (Text-fig. 1-4.) 



Undetermined Brachiopod of the Strophomenacea, 1921, 

 H. Bekker, " The Kuckers Stage of the Ordovician Rocks of North- 

 East Estonia," Acta et Commendationes Universitatis Dorpatensis, 

 A ii, 1, p. 77, pi. i, figs. 13-14 ; pi. iv, fig. 13. 



Diagnosis. — Outlines of valves, which are normally concavo- 

 convex, rounded-quadrangular, widest anteriorly. Area nearly 

 straight, that of the ventral valve more elevated and the umbo 

 of this valve slightly produced above the area. Visceral fields 

 broad, clearly marked, elliptical. The muscular region of the 

 ventral valve in the umbonal cavity, surrounded by elevated dental 

 lamellae. In the dorsal valve a platform for the adductors, the 

 cardinal process trifid. 



Material. — Author's collection in Tartu, Estonia : two ventral 

 valves, one dorsal valve. Three ventral valves and three complete 

 specimens in the Geological Museum, University of Tartu. 



Locality and Horizon. — Kohtla-Jarve, Kuckersite quarry. 

 Kuckers stage, C 2, Ordovician. Tallinn (Estonia) ; Pavlovsk 

 (Russia), C 16. 



Dors. V. Ventr. V. 



Measurements. — Width at hinge-line . 19*5 mm. 23*5 mm. 

 Greatest width . . 20 23*5 



Length . . .16 20-5 



Description : Ventral Valve. — The area is slightly triangular, 

 delthyrium moderately broad. Shape of the teeth not seen, as the 

 valve unfortunately is slightly weathered, but they are supported 

 by rather strong dental lamellae (Fig. 3) ; two curved ridges touch 

 the dental lamellae anteriorly, enclosing the muscular area and a 

 slightly elevated septal process, which j^roceeds anteriorly from 

 the muscular area, dividing nearly in the middle of the length of the 

 shell, and encircling two large elliptical visceral fields ; these show 

 shell-callosities, a number of more or less parallel wrinkles (? ovarial 

 markings). The muscular area shows marks of the diductors as 

 well as accessory diductors ; the diductors enclose adductor marks. 



Dorsal Valve. — Has an almost straight area, slightly inclined 

 towards anterior end (Fig. 2). The trifid cardinal process is elevated 

 above the hinge-line, and shows anteriorly two well-developed 

 grooves ; on its back it shows mark of the diductor scar (Fig. 1). 



