Weyenbergh,] 816 [February 20, 



macroscopic observations. It may not be amiss to remark that, in the 

 thin section, the Rockport granite is a much tougher rock than the 

 Quincy syenite, and can be ground much thinner without breaking. 



The dikes examined were all of a basaltic character, and the east 

 and west, or older ones, will in general be classed as diabases, and 

 the younger as melaphyrs; but the distinction between them is much 

 less marked than is the case in the same rocks in the vicinity of 

 Boston. These old dike rocks are in many cases much less altered 

 than are some of the recent basalts of California. Most of the 

 boulders in the parts of Rockport that were visited, are local, and in 

 a great measure nearly in situ, as can be readily seen upon almost 

 any part of the Cape. 



On two New Species of the Genus Pachylus Koch, from 

 the Argentine Republic. By Prof. H. Weyenbergh, Ph.D. 



Pachylus mesopotamogalis m. P. corpore sphaero-triangu- 

 lari, prope subovato ; cephalothorace margine laterali irregular iter 

 granoso ; mandibulis et palpis feriTugineo-fuscis : intra ocuios nee non 

 in ultimo cephalofhoracis segmento spina acuta : omnium prope spina- 

 rum apicibus claris ; femoribus spinosissimis et curvatis; articulaiion- 

 ibus pedium omnium circulo claro ornatis ; tarsis l l paris ex 6, 2 l ex 8, 

 3 li et 4> l ex 6 ariiculis constanlibus . 



d". The general color is sepia. The palpi light brown, six- 

 jointed, with a sharp nail on the last joint; three spines on the 

 inner side of the penultimate, and four on the same side of the fol- 

 lowing joint. The posterior spine of each joint is the largest, regu- 

 larly decreasing in size toward the apex of the palp. The mandibles 

 are also light brown or yellow; the outer (movable) blade of the 

 pincers of the mandibles is stronger than the inner. 



The first three legs are sepia-colored, a little warty, but these 

 warts are very small. The tarsi are a little lighter, especially those 

 of the fourth pair. The trochanters are light brown, and around 

 every articulation of the leg is observed a circle of the same color. 

 The eye-tubercle is distinct, and a sharp black spine with a light 

 brown tip lies between the two eyes. This part of the cephalo- 

 tliorax is dark ; the following part, consisting apparently of five 

 segments, is lighter, and a longitudinal impression in the middle of 

 the back divides it into lateral halves, so that the first of these five 

 segments is more or less polygonal in form on either side ; the whole 





