srrciKs or PISIDITM. 101 



Schmidt's original description (156, p. 119) is as follows : 



" Vorder- und Hinterseite des Oberrandes stossen in den 

 Wirbeln recht-, ja selbst spitzwinklig zusammen ; auf den 

 Wirbeln befindet sich erne scharfe llunzel ; das kurze Ligament 

 springt deutlich vor ; Schlossziihne unverhaltnissmassig dick; 

 dabei i&t die kleine Mnschel so bauchig und der Vorderrand 

 so weit vorgestreckt, dass sie sich gern auf das Vorderende des 

 Itiickens legt und den scharfeii Unterrand emporkehrt deshalb 

 nenne ich sie Pis. siipinum" 



He adds a little later that the appendiculae on the umbones are 

 not always present. 



JBaudon's diagnosis (9, p. 362) being yet clearer we append it : 



" Concha triaugularis, obliqua,' alta, convexa ad umbones, 

 solida, subopaca, tenuiter striata, suporius conica, inferiua 

 arcuata, antice rostrata, postice vix subcurvata, pallida, corneo 

 lutea vel flavesceus; apicibus subacutis lamella superatis ; 

 liganiento brevi, lineari, flavido ; commissura crassissima, 

 pnesertim quoquoversns et undique crenulata ; duobus dentibus 

 cardinalibus, tuberculosis, vix conspicuis." 



Ho has, however, mistaken the characters of the hinge-teeth, the 

 details of which are as under : 



Hinge (PI. II, f. 5 ; IV, f. 7) nearly | the length of the shell, 

 massive, projecting well inwards, strongly arched with two 

 flexures. 



11. V. a. /. about 1 the length of the hinge-line, very stout, curving 

 sharply inwards ; base exceedingly deep, solid and 

 swollen ; apex near distal end, moderately prominent, 

 rounded obtuse ; ridges very round, sloping about 

 equally and fairly steeply. 



a. iff. about \ the length of a. ;., from which it is separated by 

 a deep fossa ; somewhat apposed to the shell-margin : 

 apex on distal side of centre, not very prominent ; 

 ridges rounded, distal short and steep, umbonal longer 

 and less steep. 



3. scarcely prominent, narrow, arcuate; a nearly parallel 

 to the shell-margin, b curving diagonally to the inner 

 margin of the hinge-plate. 



. i. length about J that of hinge-line, very strong, narrow, 

 slightly curving inwards ; base strong, swollen ; apex 

 distal side of centre, scarcely prominent, very obtusely 

 acuminate; ridges not much rounded, umbonal long 

 and gradually sloping, distal short, at tirst nearly 

 vertical, then sloping gently. 



p. in. not quite | the length of p./., narrow, somewnat 

 apposed to the shell-margin ; apex near distal end ; 



