44 



N. 10° W. ; and Nahant would be a little to the east of north. 

 The Braintree rocks would then dip under those of Nahant, 

 unless the same formation extends across the bay ; in which 

 case, the Nahant series would form its upper strata. 



The existence of these Paradoxides in the argillaceous slates 

 of Braintree, proves them to belong to the lowest of the fossil- 

 iferous Silurian rocks, and that they are the geological equivalents 

 of the argillaceous slates of Sweden, which are in a similar 

 manner disrupted by the intrusion of Sienite. It is certainly 

 interesting to find the base of the silurian system resting within 

 the limits of old Massachusetts. 



The President stated that he had recently examined 

 the electric apparatus in the tail of one of our common 

 skates {Raia Icevis). 



The electric organs have been noticed by several anatomists, 

 but have been fully described in Raia hatis and other species by 

 Robin. . In the species dissected by Dr. Wyraan, the organs 

 were more largely developed, extended further up into the base 

 of the tail, and were more uncovered by the muscles, posteriorly, 

 than in the ones examined by Robin. Thus far, no positive proof 

 has been adduced to show that the organs in question really 

 constitute an electric apparatus. Structurally they resemble 

 those of the Torpedo and Gymnotus, but have not been observed 

 to evolve electricity, though it has been stated that if a living 

 skate is held by the tail, an electric shock is felt. 



The President also stated that he had seen the horny shell of the 

 egg of the skate in the process of formation. He had found one 

 in each oviduct, surrounded by the glandular enlargement which 

 is visible near its middle. That portion of the duct was very 

 much thickened, and mainly consisted of long tubular follicles, 

 opening into its cavity. Although the shells were partially 

 formed, the yolks had not yet descended into the duct; many of 

 them were nearly mature. If this be a normal state of things, 

 then we have, thus far, an unobserved example of the shell 

 being formed previous to the descent of the ovum. The shell 

 forms a pocket, open at the upper extremity, and through this 

 opening, which is never wholly closed, the egg probably descends 

 into its cavity. 



