108 



SUPPLEMENT TO THE 



Whitjieldia twmida. 



Loop and attacbments to tlie liinge-plate, after 



Mr. Glass's preparation. 



He has likewise been able to work out the attachment of the principal stems to the hinge- 

 plate and their complicated system of connecting lamellse. 



In the interior of the dorsal valve the prin- 

 cipal stems are attached to the hinge-plate 

 (at a). After extending slightly downwards 

 under the beak of the ventral valve for a 

 short distance, their extremities {b) suddenly 

 bend backwards towards the lateral portions 

 of the valve in the shape of the letter V, the 

 outer branches forming a broad curve facing 

 the bottom of the dorsal valve. These primary 

 stems gradually converge to about half their 

 length, and then diverge again near the 

 front, thus forming the first coil of the 

 spirals. At about half their length (at d) 

 the lamellse widen, and they each give off 

 another lamella {d, h). These lamellas con- 

 verge from both sides, and in an inward direc- 

 tion towards the middle of the interior of the shell and between the spiral coils. After 

 the two extremities have come in contact at the point h, the conjoined lamella continues 

 in a straight direction towards the beak [h,f,) and after coming to within a short distance 

 of the point where the primary lamellse are attached to the hinge-plate, it bifurcates and 

 forms a short V-shaped process {g). 



In addition to the specimens figured, Mr. Glass made several additional preparations 

 in order to discover whether the lamellae forming the V-shaped or forked process {g) had 

 any further extension, as figured by Professor Hall in his genus Meristella {31. arcuaid) ; 

 but he could discover no trace of any similar extension. 



In 1880 Professor Hall kindly sent me some specimens of his so-termed Meristina 

 Maria, and I was at once struck by the complete identity of its exterior form with the 

 Atrypa tiimida of Dalman ; and Mr. Whitfield agreed with Mr. Glass and myself in thinking 

 that they belonged to the same species. Shortly afterwards Mr. Glass worked out a 

 typical specimen of the American species which had been given to me by Professor Hall 

 for that purpose (' Sil. Sup.,' PI. V, fig. 6), and it very plainly showed that 

 the connections of the spirals are identical in Whitfiehlia tumida and its synonym, 

 Meristina Maria. In the American description of the interior of Meristina JSIaria the 

 loop is said to be simple ; but it is now proved by Mr. Glass that the end of the loop was 

 bifurcated, and in exact agreement with the figure we have given of the same part in 

 Wldtfieldia tumida. Through the kindness of Mr. Whitfield we have been able to 

 examine the original specimen from which Professor Hall's figure and description were 

 taken, and this evidently shows that the mistake had arisen through Mr. Whitfield haying 



