156 J. WILFRID JACKSON ON 



ances are concerned, with the recent examples described above from South Orkneys. 

 The shell-punctse and internal characters (the latter unfortunately unknown so far in 

 the fossil form), may, however, prove them to be quite distinct. 



The fossil examples were obtained at Cockburn Island, oft' Graham Land, in strata 

 referred by BUCKMAN to Miocene-Oligocene age. 



Liothyrina blochmanni, n. sp. (PI. I. figs. 4-8.) 



Shell somewhat pear-shaped, longer than wide, reaching its greatest diameter 

 towards the anterior margin. Sides of beak elongate, subrectilinear ; lateral margins 

 convex, merging insensibly into the frontal border, which is rounded. Line of joining 

 of valves somewhat flexuous. Valves swollen, without plication or sinus ; the ventral 

 slightly deeper than the dorsal. 



Surface smooth, with numerous very fine growth lines and traces of extremely fine 

 radiating striae which appear to arise from the radial arrangement of the punctse.* 



Test very thin, glassy, and almost transparent ; visibly punctate. Colour whitish. 



Shell-mosaic very clear and distinct ; regularly developed. Pores per square milli- 

 metre =60 to 80. 



Ventral valve with a short beak, incurved, truncated by a moderately large, circular, 

 collared foramen, bounded below by two joined deltidial plates. Sides of the beak 

 well rounded. In the interior, teeth small and placed in immediate contact with the 

 basal angles of the deltidial plates. No dental plates. Umbonal cavity very deep. 

 Internal surface completely smooth. Muscular impressions very weak. 



Dorsal valve very convex, with a linguloid nucleus. Interior smooth. Slight 

 median septum extending from adductor muscular impressions almost to the apex of 

 umbonal cavity, its total length being about a quarter the length of the valve. 

 Muscular impressions clear but not deeply marked. Cardinal process small but quite 

 distinct ; flattened and transverse. Cardinal apophysis weak, composed of two 

 divergent and flattened triangular plates, the external borders of which limit the 

 dental sockets ; the inner borders form the base of the crura. The brachial apparatus 

 commences with short crura, which bear wide, triangular crural processes with their 

 points directed somewhat ventrally. The descending limbs are remarkably parallelt 

 The transverse band is short but fairly broad, and is slightly indented in the middle 

 portion ; point of junction with descending branches well rounded. 



Dim. Size of the largest example (type) : length, 23 mm. ; breadth, 19 mm. ; thick- 

 ness, 12 '5 mm. 



Hob. Station 417 ; lat. 71 22' 8., long. 16 34' W. (off Coats Land). Depth, 1410 

 fathoms. March 18, 1904. Sea bottom, blue mud and stones. Temperature 29 "9 F. 



Obs. Two almost perfect examples, together with a single dorsal valve and the 

 hinge portion of another, were brought up by the trawl at this station. 



* This radiating striation can only be seen in a good light and when the shell is held at a certain angle, 

 t Recalling DAVIDSON'S figure of L. sphenoidea in Recent Brachiopudu, pi. ii. fig. 18. 



(BOY. soc. KDIN. TRANS., VOL. XLVIII., 378.) 



