C. E. Beecher — Development of the Brachiopoda. 133 



ments could be made. Those which were chosen as funda- 

 mental are : 



m*m, 110^110 = 90° 12' m*p, 110 a 221 = 24° 37' a~p, 100 a 221=49° 53' 



The axial ratio and forms are as follows : 



^ : i; S =0-9965: 1: 0-7698 /3 = 100^001 = 89° 531'- 

 a, 100, i-l m, 110, I d, 403, — A-I s, 403, |4 jp, 221, —2 



c, 001. n, 130, 2-3 e, 203, —%-% u, 203, £-i o, 263, —2-3 



The pyramids^? and o were frequently wanting. The ortho- 

 domes d, e, s and u were very constant in their development 

 and gave to the crystals an orthorhombic habit. Owing to the 

 curved and striated character of the faces the symmetry could 

 not be satisfactorily determined by measurement, but the 

 optical properties showed that the crystals were truly mono- 

 clinic. In polarized light the tables show an extinction par- 

 allel to the ortho- axis and in convergent light one of the 

 optical axes and the acute bisectrix can be seen near the 

 limits of the field. The plane of the optical axes is the clino- 

 pinacoid. 



These two salts, although entirely different in crystalline 

 habit, are very similar in their axial ratios. 



Sheffield Scientific School, 

 April, 1892. 



Art. XIX. — Development of the Brachiopoda. Part II. 

 Classification of the Stages of Growth and Decline ; by 

 Charles E. Beecher. (With Plate I.) 



A brief review of the known embryology of the Brachi- 

 opoda is desirable, in order to account for some of the differ- 

 ences presented by adult forms in the several divisions of the 

 class. This knowledge is far from complete, and is confined 

 to a few species, but much of interest bearing on the later 

 development of the organism may be obtained. 



The important memoirs of Morse," 18 ' 19 Kovalevski, 15 

 Lacaze-Duthiers, 16 and Shipley, 22 contain nearly all that is 

 known regarding the early embryology of brachiopods. The 

 genera included in the works of these authors comprise 

 Cistella, Terebratulina, Liothyrina, and Lacazella. Later 

 larval stages of the genus Glottidia have been fully described 

 by Brooks. 4 Miiller, 20 also, has given a description and figures 



*The works referred to by numbers are cited in full in the list appended to 

 this article. 



