Palaeozoic Arachnida of North America. 93 



traceable on the dorsal side, the first of the seven (/. e. the seventh 

 counting forwards from the posterior end) being almost invariably 

 longer than those that succeed it ; each tergum is marked on each side 

 with a longitudinal sulcus or groove which separates a lateral lamina 

 from the median area of the tergum ; sometimes there is a second 

 sulcus nearer the external margin than the one just mentioned ; hence 

 each tergum is divided into either three or five distinct areas according 

 to the number of sulci. In front of the seventh tergum from the end, 

 either one ot more tergal sclerites may be traced ; these are usually 

 not provided with lateral laminae and may be overlapped more or 

 less by the posterior border of the carapace ; they appear to represent 

 from one to three additional tergal plates undergoing excalation. 

 The last tergal plate on the dorsal side, that is to say the seventh, not 

 counting the variable number of anterior tergal plates just mentioned, 

 is the narrowest of the series ; but it is almost invariably provided with 

 an unpaired posteriorly-expanding median lamina, in addition to its 

 paired laminae. With which it forms a continuous series ; this lamina 

 is itself sometimes marked off by a transverse sulcus from the median 

 area of the tergum. This median lamina of the last tergum visible 

 from the dorsal side, overlaps the tergal element of the next succeeding 

 segment ; the tergum of this segment is fused with its sternal element 

 to constitute a subannuliform sclerite, near the center of which lies 

 a plate, the anal operculum, which is the tergal element of the last 

 segment. Thus ten tergal elements may be traced with certainly 

 in almost all genera, the last being the anal operculum and the first 

 the short tergal area that lies between the carapace and the first large 

 tergal plater of invariable occurrence, namely the seventh from the 

 end on the dorsal side. 



" The sternal elements of the opisthosoma appear to correspond 

 in number With the terga, except that, with the doubtful exception of 

 Eophrynus, there is no sternal plate to represent the tenth tergum 

 or anal operculum. Hence there are nine sternal plates in all, the 

 last being the ventral element of the plate surrounding the anal oper- 

 culum. The anterior sterna are variously modified and arranged 

 according to the genus, the arrangement in Anthracomartus being very 

 different from that of Eophrynus, the first, whether large as in the 

 former or small as in the latter, being probably the genital oper- 

 culum." 



Not having sufficient material to make a study of the morphology 

 of the abdomen in Anthracomarti, I am not able to either accept or 

 criticize Pocock's interpretation. One point, however, I cannot 

 leave without mention. If Pocock's interpretation is correct and 



