Palceozoic Bivalved Entomostraca. 411 



vern. Messrs. Vine and Smith have found many individuals, 

 and added to the number of known species, tliongh their col- 

 lections do not appear to contain an example of Jones and 

 HoU's second species, namely ^chmina clavulus. It may be 

 added that some of the present specimens show a delicate 

 serration of the free margins (see figs. 5 a, 5 c, and 9, PI. XIII.). 

 This ornament is more perfect and delicate in some Scandi- 

 navian specimens, exquisite drawings of which have been 

 sent by Dr. Lindstrom. 



] . ^ckmina cuspidata^ J. & H. 

 (PI. XIII. figs. 2, 3 a, 3 ^'j 4 a, 4:b,4c, and 9.) 



ALchmina cuspidata, J. & 11., op. cit. p. 218, woodcut, fig, 2, and pi. xiv. 



tig. 8. 



Proportions : — 



Thickness at the Width between 



root of the the ends of 



Length. Height, spikes. Length of the spike, the spikes. 



Fig. 8: 28i 15 10 ^^ <",frlf f«='} 83 



Fig. 4 : 22 1 12 8 23 84| 



Only a fragment of this delicate form was met with and 

 described in 1869. The woodcut referred to gives the form 

 of its valve, and the present figs. 2, 3 a, and 9 correspond 

 with it. The position of the stout, sharp, hollow spike is also 

 the same. The specimens before us show beautifully the 

 exact proportions, direction, and length of these remarkable 

 horn-like processes of the valves. 



There are some slight differences between fig. 3 and fig. 4, 

 as to both the lieight of the valve and the angle of direction 

 and of divergence in the processes. In fig. 4 the valve is not 

 only smaller, but it is relatively more contracted anteriorly, 

 the antero-ventral margin being less convex than in fig. 3 a, 

 and the posterior margin projects more in the middle than 

 above. The spike also is not so upright as in figs. 2 and 3 a, 

 but leans more forward ; and it had a rather more open angle 

 of divergence from its fellow when the valves were closed, as 

 may be seen on a comparison of fig. 4 h with fig. 3 h. These 

 diff"erences, however, may be sexual or the pecuHarities of 

 individual growth. Angle of divergence in fig. 3 h (1) at the 

 top of the valve 45°, (2) taken from the middle front of the 

 valves 58° ; in fig. h, (1) 40°, (2) 50°. 



The end views may be roughly compared with a three- 

 rayed star, in which the lower portion is somewhat shortened 

 and very much thickened. 



