28 CATALOGUE OP 



on it was preoccupied by A. Braun (24, p. 1116) fur a Miocene 

 form, subsequently figured by Sandberger (153, pi. xxvi, f. 7), so 

 that its present name conferred by Dr. F. Sandberger in 1880 (154 A, 

 p. 96) stands. His description, founded on specimens from the 

 original locality of West llunton, reads : 



" Testa solida, subcordiformis, extus costis concentricis 

 imbricatis distantibus ornata, sulcis latis subtiliter striatis 

 disjunctis. Umbones luti, depressi, submediani ; fossula liga- 

 mentalis brevis, sat profunda. In valva dextra dens cardinalis 

 posticus tenuis obliquus et anticus bifidus, compresso-trangu- 

 laris, in sinistra posticus tenuis arcuatus et anticus crassus 

 bifidus, obtuso-triangularis conspiciuntur. Dentes laterales 

 diversi, inferi in valvis ambabus conformes, obtuso-triangu- 

 lares prominuli, superi in dextra solum conspicui et fossulis 

 sinistrae excepti parvuli, obtusi. Alt. 7, Long. 9, Crass. 

 5 mm." 



It will be noticed that Sandberger has confused the left and 

 right valves, forgetting for the moment the peculiar conformation of 

 the shell in this genus, and further deceived by the deep notch in 

 the cardinal tooth (3) of the right valve describes it as two. 



The details of the hinge are as follows : 



Hincje (PL I, f. i! ; III, f. 2) about | the length of the shell, 

 broad, not projecting much inwards save at the umbo, strong, 

 well curved, with two marked flexures in the right valve. 



R. V. a. r. about g the length of the hinge-line, very stout and 

 strong, curving inwards ; base very strong and swollen, 

 especially on the umbonal side ; apex central, very 

 prominent, inclined im\ards, rounded obtuse; ridyes 

 rounded, sloping about equally and not very steeply, 

 the umbonal descending a little lower than the distal. 

 a. in. about halt' the length of . /., from which it is separated 

 by a deep sulcus, stout, strong, erect, curving with the 

 shell-margin ; apex about central, prominent, rounded 

 obtuse; ridges somewhat rounded, descending about 

 equally and fairly gradually. 



3. sharply curved and flexed, strong, prominent, flat- 

 topped, notched at the angle, a slanting diagonally 

 forwards across the hinge-plate, b similarly inclined 

 backwards, slightly wedge-shaped and deeply sulcate. 

 p. i. about 3 the length of the hinge-line, fairly stout, very 

 strong, distal end curving inwards ; base very strong, 

 slightly swollen ; apex central, very prominent rounded 

 obtuse ; ridges somewhat rounded, descending about 

 equally and fairly steeply. 



/>. ///. about I the length of p. /., to which it is slightly inclined, 

 their umbonal extremities tending to become confluent, 



