108 CATALOGUE OF 



Morch's diagnosis (121, p. 37) is a little more explicit: 



" T. oblique-ovalis, ventricosa, striis increment! subtilissimis, 

 sulci increment! 5-6 rernoti contasbulati [sic], cinereo-lutes- 

 cente, intus cinerea ; umbones gibbosi." 



But Clessin's description of his Pisidium ylobidare (179, p. 532), 

 which comparison of authentic specimens shows to be the same, 

 conveys a more accurate notion : 



"Concha mediocris, rolundato-ovata, tennis, subtiliter stria ta 

 flavo-cornea ; umbones prominentes, lati, rotundati ; liga- 

 mentum contectum ; dentes card. valv. sinistra? 2, posterior 

 brevis, tunuis, vix cnrvatus, anterior crassus, in angulum 

 curvatus, dens card. valv. dextree curvatus, parte posteriore 

 brevi, crassiore, parte anteiiore longiore, tenui." 



To this again must be added the details concerning the characters 

 of the hinge : 



Hinge (PI. II, f. 7; IV, f. 1) about f the length of the shell, 

 not very broad and not projecting much inwards, strongly 

 arched. 



11. V. a. I. about 3 the length of the hinge-line, narrow, fairly 

 strong, slightly deflected inwards ; base j'airly strong ; 

 apex central, prominent, acuminate ; ridyes fairly 

 sharp, sloping about equally and steeply. 



a. in. about ^ the length of, and parallel to a. /., narrow, 

 straight, inclined toward .the shell-wall ; apex distal 

 side of centre, pointed, obtuse ; ridyes somewhat 

 rounded, descending equally and gradually. 

 3. lamellit'orm, prominent, anterior end higher, sharply 

 flexed; a fairly parallel to the shell-margin, b running 

 diagonally across the hinge-plate to its margin. 

 j>, 7, not quite 3 the length of the hinge-line, narrow, fairly 

 strong, straight ; base not strong ; apex nearer distal 

 end, fairly prominent, pointed, obtuse ; ridyes sharp, 

 sloping about equally and fairly gradually, 

 p. in. about -|- the length of, and parallel to p. /., narrow, 

 fairly strong, straight; apex about central, obtuse; 

 ridyes somewhat rounded, sloping about equally and 

 fairly gradually. 



L.V. a. n. about 1 the length of the hinge-line, narrow, fairly 

 strong, curving with the shell-margin ; base fairly 

 strong; apex central, very prominent, very acuminate, 

 slightly distally directed; ridges fairly sharp, distal 

 exceedingly steep at first, then sloping gradually, 

 umbonal steep. 



~. triangular, prominent, base continuous with that of 

 a. if., apex backwardly directed. 



