142 E. Lewis— Water Courses on Long Island. 



ring is not, as I originally believed it to be, firmly soldered to 

 the pygidium. 



It is a remarkable fact that, under each of the four trilobitic 

 genera represented in the Troy Primordial, viz.. Obutllns, Conn- 

 rodiscus and Agnostus, there should be found, in this 

 fauna, a species affording an example of a well-marked depart- 

 ure from the usual structure of the genus to which it belongs. 

 Thus Microdiscus speciosus has but three body-rings, as already 

 stated, while all the other described species of the genus whose 

 thorax is known have [our: Agno-tus imbilis has but one body- 

 ring, while nearly all of the other species have two ; Conocorypke 

 tri/iiitala. ; [t caudal margin stands widely 



apart from all the other certainly known species of the genus ; 

 while Olenel ike the other described species in 



which the thorax has been observed, has none of its anterior 

 pleurae extravagantly prolonged as compared with the others. 

 In this respect this latter s] eeies, as Barrande has already indi- 

 cated, sustains the same relation to the Vermont forms of the 

 do the Swedish Paradoxides to their Bohemian allies. 



ART. XVIIL— On Water Courses upon Long Island; by ELIAS 

 Lewis, Jr. 



It has been estimated that of the forty-two inches of average 

 annual rainfall upon Long Island more than three-fourths -inks 

 directly into the porous soil. The excess which occurs when 

 the fall is unusually heavy, or the surface frozen, makes its 

 way into the innumerable valleys which traverse its surface. 

 These valleys may therefore be considered as lines of surface 

 drainage, the principal of which have their source on the 

 high grounds near the center of the island, whence a portion of 

 them extend northward toward Long Island Sound, others 

 southward to the bay or ocean. 



On the r>< nd, of which we shall first speak, 



many small lateral valleys open into the larger ones, cutting 

 the surface into a series of valleys and hills, forming a land- 

 scape exceedingly beautiful and picturesque. 



The high grounds referred to comprise a range of hills which 

 extend more than sixty miles in a direction parallel with that 

 of the island, and which vary from 150 to 384 feet in height. 

 je is called, absurdly enough, the backbone of the 

 island. It consists, however, of glaciai drift, with boulders, many 

 of immense size, but is wholly without rock in place. It is 

 upon this range, quite at the top in many instances, that the 



