162 



Bashford Dean Memorial Volume 



Text-figure 44. 



The median-dorsal plate seen from the 



inside. 



adl, part overlapping ADL: pdl, part overlap- 

 ping PDL; ti;, posterior thickened part of longi- 

 tudinal keel. 



distinct overlapping impression. This part of MD covers ADL and PDL. The margin 

 overlapping ADL .is placed on the front angle of MD (Text-figure 44 adl). It is smaller 

 than the margin overlapping PDL (Text-figure 44 pdl) from which it is well separated. 

 The last goes very far backwards and stops near the median line. The sharp and relatively 

 deep grooves on the surface of the overlapping margin, demonstrate clearly how solidly 

 these three plates were connected. 



Along the median line on the underside of MD rises the well known longitudinal 

 keel. It begins nearly on the front margin, and, rising gradually, runs backwards. It 

 continues quite far back behind the hind margin of MD. Its posterior margin is massive 

 and forms a rounded thickening (Text-figure 44 t\). This thickening is broadest at the 



