42 



TERRESTRIAL CARBONIFEROUS ARACHNID A. 



one case ten terga on the dorsal side, and always a small anal operculum beneath 

 the last, but on the ventral side. Thus eleven segments are traceable in the 

 opisthosoma. The number of sterna is doubtful ; but there appear to be at least 

 nine, excluding the area between the coxae of the last pair of legs, the first sternal 

 plate being large with a widely convex posterior edge and the last small and 

 encircling the sides and lower edge of the anal operculum. Mandibles or cheliceras 

 not fully known, but their basal segment elongate and porrect. Palpi short and 

 pediform, consisting of six segments, the basal segment (maxilla) the largest, not 

 concealed from below, and slightly divergent from its fellow of the opposite side. 

 Legs of the first pair long, somewhat like those of the Thelyphonida?, the terminal 



Fig. 15. — Plesiosiro madeleyi, gen. efc sp. n. ; dorsal 

 surface with appendages restored from several 

 specimens, four times nat. size.— Coal Measures; 

 Coseley, near Dudley. 



Fig. 16. 



the same. 



segments (protarsus and tarsus) converted into a seven- jointed tactile organ, 

 apparently without a claw ; the rest of the segments normal in number and 

 structure. The remaining legs ambulatory, similar in form and in segmentation, 

 each consisting of the normal seven segments characteristic of the Arachnida, the 

 patella being short and the terminal segment (tarsus) undivided. Claws unknown. 

 The basal segments large, those of the fourth leg the largest, separated in the 

 middle line by an elongated sternal area which seems to expand behind between 

 the coxae of the fourth pair. Sternal plates of prosoma unknown, except for a 

 small triangular anterior sternal plate lying immediately behind the basal segments 

 of the palpi, and between those of the legs of the first pair and partially also 

 between those of the second pair. Position of generative orifice unknown. 



