1887.] ill- [Kirkwood. 



have that regular tricuspid division of the crown which is first observed in 

 the genus Ampliileates of the English Lower Jurassic and characterizes a 

 large number of the Jurassic mammals. 



EXPLANATION OF PLATE. 



Figure 1. Microconodon tenuirostris. The outer surface of the right 

 mandibular ramus, enlarged. The two premolars preserved are the first 

 and third, with the fang of the second between. The space behind the 

 third was occupied either by a fourth premolar and the first molar, or by 

 the first and second molars. The molars preserved are, therefore, either 

 the second and fourth, or the third and fifth. The dotted outlines are 

 purely conjectural, 



\a. The same, natural size. 

 16, The fourth or fifth molar, much enlarged. 

 Figure 3, Dromatherium sylvestre. The inner surface of the left man- 

 dibular ramus, enlarged. 



2a. The same, natural size. 



2b. The second molar, much enlarged. 



ABBREVIATIONS. 



a. Angle ; c. canine ; en. condyle ; cr. coronoid ; i. incisors ; v)(/. my- 

 lohyoid groove ; to. molars ; p. premolars. 



The Relation of Aerolites to Shooting Stars. 



By Professor Daniel Kirkioood. 



■iEead before the American Philosophical Society, April 15, 1887. ) 



The writer more than twenty years since gave reasons for believing that 

 shooting stars, fire balls and meteoric stones move together in the same 

 orbits.* The facts then collected were deemed sufiicient to sustain the 

 theory advanced, or at least to give it a high degree of probability. This 

 view has been rejected, however, by several eminent astronomers, and 

 especially by the present Astronomer Royal for Ireland, the distinguished 

 author of " The Story of the Heavens." He remarks: "It is a notice- 

 able circumstance that the great meteoric showers seem never yet to have 

 succeeded in projecting a missile which has reached the earth's surface, 



* Meteoric Astr,, Chap. v. 



