168 



Bashford Dean Memorial Volume 



The overlapping margins on the inside of AL (Text-figure 52) are 

 distinctly developed. They occupy the hind portion of the upper part of 

 AL. From the upper angle (ua) their edge extends downward nearly two- 

 thirds of the length of the whole plate (a). From here it curves very 

 sharply upward a short distance ia-b), and then again turns downward 

 (b-c). Finally, it meets the hind margin of the plate a Httle below the 

 mentioned projection (s). The long cuneate part of the not overlapped 

 surface, defined by a-h-c divides the overlapping margins on AL in two 

 parts: one, the larger (Text-figure 52 ADL), overlaps ADL and, as we 

 know, IS very solidly connected with it; the other overlapping margin 

 covers PL. It is smaller and less ridged (Text-figure 52 PL). 



The most interesting thing in AL is the previously mentioned 

 inner wing (C). It begins as a thickened ridge at the upper angle of the 

 plate and runs at first nearly vertically downward. Near the middle of 

 the plate it curves'forward' and downward (Text-figures 51, 52 and 53 x). 



Between it and the other part of the plate a groove 

 is formed, which becomes larger and larger as it 

 extends forward (y). The upper part of this 

 groove is occupied by a roundish thickening (th), 

 which gradually disappears upward, but is sharp- 

 ly defined downward (Text-figure 53). In the 

 lower part, the wing itself is quite broad and thin, 

 its upper margin running nearly parallel to that of 

 the lower part of AL. It ends in a rounded point 

 (z) far behind the surface of AL. Its lower margin 

 arches to the front point of the lower part of AL. 

 If we look at the section through the 

 lower part of AL and the wing (Text-figure 51 

 a~h), we notice that the bottom of the groove between them is quite thin (ht). Thus 

 there is formed from beneath a deep impression (im) between the inner surface of the lower 

 part and the bottom of the wing. This whole division is S-shaped in section, and not 

 especially solidly built. It is, therefore, comprehensible that it is nearly always strongly 

 compressed in fossil e.xamples and as a rule the wing is pressed against the underside of the 

 lower part, and the connection totally destroyed. But in some specimens this part is well 

 preserved and in others it can easily be rebuilt. For example, the clavicular of Dinichthys 

 magnificus Huss. & Bry., figured and described by Hussakof and Bryant (1918, p.. 42;" 

 PI. 7, fig. 2), shows the grooves between the wing and the lower part of AL very distinctly. 

 Thus (erroneously) the structure of AL in Dnnchthvs seems unusual. The structure ot 

 this part of the Arthrodiran carapace is difficult to study. Very often, especially in small 

 forms, the limits and outlines of the intero-lateral and spinal are indistinct, and it is 

 therefore difficult to determine the boundaries of AL. However, in Coccosteus decifiie?!.': 



Text-figure 53. 



The antero-lateral plate in front view. 



A, upper part; B, lower part; C, hind wing; d, curving 



point of front margin; rh, thickening between A, B and 



C, ua, upper angle; x, curving point of hind ridge; v, 



groove between A, B and C; z, front part of C. 



