cope.] ^'^^ [August 19, 1870. 



The procitic is a distinct though small bone, below and in front of the 

 squamosal. The presphenoid is plate like, and much as in the Croc- 

 odilia. 



Prof. Cope thought that the Anomodontia, one of the earliest (Triassic) 

 types of Reptilia are one of the best examples of a generalized group 

 among tlie vertebrata. Thus the structure of the posterior part of the 

 Cranium is largely that of Ichthyopterygia, and partially that of Lacer- 

 tilia ; of the oral parts of the cranium, the prootic and mandible, of 

 Testudinata. The vertebral characters are partly those of Ichthyoptery- 

 gia, and the sacrum and rib articulations those of Dinosauria. The pe- 

 culiar pre.sphenoid is characteristic of Crocodilia, and the osseous inter- 

 orbital septum, of the Rhynchocephalia. 



The position of the posterior plate of the squamosal in Ichthyopterygia 

 and Anomodontia seemed conclusive as the homology of that element with 

 the bone covering the cartilaginous quadratum in Batrachia Anura, and 

 the osseous quadratum in Urodela and Dipnoi, called tympanique by 

 Cuvier, and temporo-mastoidean by Duges. This bone had been already 

 homologized with the preoperculum of Teleostei by Huxley, and it is 

 thought that its present determination in the Reptilia established the serial 

 homology of the preoperculum of the fish witli the squamosal plate of 

 the mammal. 



Prof. Kirkwood communicated a paper " On the Mass of 

 the Asteroids between Mars and Jupiter." (See Proceedings 

 below.) 



Prof. Cresson described the thunder storm of the 4th inst. 

 at the Belmont Water Works. 



And the Society was adjourned. 



On the MASS of ASTEROIDS beticeen maks and jupitek. By Pko- 

 FESSOR Daniel Kirkwood, Bloomington, Indiana. 



According to Leverrier, the total mass of the ring of minor planets does 

 not exceed ^th of the earth's mass, or yaV o^b of that of Jupiter. So great 

 a disproportion between two adjacent planets is without a parallel. Is 

 the fact susceptible of a probable explanation ? 



Were the sun transformed into a gaseous spheroid with an equatorial 

 radius equal to the diameter of the earth's orbit, a large number of the 

 known asteroids would, in perihelio, j)lunge into the solar mass and be 

 reunited with it. 'Now this, in all probability, is precisely what occurred 

 soon after the abandonment of the asteroid zone, while the solar nebula 

 was in the process of condensation. The jaowerf ul mass of Jupiter would 

 produce great eccentricity in parts, at least, of the primitive ring. Large 

 portions of its matter, or a considerable number of minor planets in a 

 state of vapor, may thus have been precipitated upon the sun before the 

 latter had contracted within their jjerihelion distance. Thy small mass 

 of Mars may perhaps be accounted for on the same hypothesis. 



