244 li. I. POCOCK. 



third pairs of lateral processes seen in Thely plionns and 

 Spiders is obvious, and is fortified by the evidence favouring 

 the view that in the spiders at least these processes cori-e- 

 spond with the second and third pairs of post-oral appendages. 

 It is onlv necessary to horaologise the muscle-bearing stump 

 in Limulus Avith the fourth lateral process in Thelyphonus 

 and the Spiders, and the strong postero-lateral apophyses in 

 the entosternite of Limulus with the vestigial processes on the 

 posterior lobe of the entosternite in Thelyphonus to com- 

 ]ilete the parallel. On the underside similarity between the 

 entosternite of Limulus and the Arachnomorphous Spiders is 

 to be found in the absence of ventral apophyses, with the 

 exception that in L. poly ]ihein us a single abbreviated pair is 

 present at the posterior end of the plnte exactly .as in some 

 of the Mygalomorj)hous Spiders, e.g. K phebopus. 



The entosternite of Scorpions has been so affected by tlie 

 compression of the prosoma that it is not easy to bring it into 

 exact line with those of the orders hithei'to considered where 

 a more primitive condition persists. That the anterior bars 

 framing the pharyngeid notch are comparable to those of 

 liimulus, the Pedi]ial]ii, and Aranese liardly admits of a doubt 

 (Tjankester, 6, 6, and 7). Similarly the lateral tendinous 

 crest supporting the leg-muscles, and so well developed in the 

 l^uthidas and Vejovidfe, foicibly recalls that of the Aranete. 

 Biit the dorsal apophyses which form so conspicuous a feature 

 in the entosternite of the Pedipalpi and the Araneie reniiiin 

 undeveloped. They are represented by the two pairs of 

 dorso-ventral muscles which lie in front of the diaphragm, 

 those of the third pair which perforate this partition being 

 usually regarded as the tergo-sternal muscles of the genitiil 

 or fii'st somite of tlie mesosoma. 



To which three of tlie four or five pairs of dorsal apophyses 

 present in the Aranene and Pedipalpi do these two pairs in the 

 scorpion correspond ? Probably,! think, to the fourtli and 

 lifth pairs, — tliat is to say, to those that belong to the fiftii and 

 sixth segments of the prosoma. 'J'his homology is suggested 

 by their position at the posterior extremity of the prosoma. 



