228 



TRILOBITA 



CHAP. 



Three types of compound eye have been recognised in 

 Trilobites * holochroal, prismatic, and schizochroal. 



1. In the holochroal eye (Fig. 139, A, B) the lenses are 

 globular or biconvex and close together, so that the cornea is 





FIG. 139. Eyes of Trilobites. (After Lindstrom. ) A, B, Sphaerophthalmus alatus, Ang, 

 Upper Cambrian. Vertical and horizontal sections, x 100. C, Asaphus faMax, 

 Dalm. Horizontal section, x 60. D, Nilcvx urnindUlo, Dalm. Vertical section, 



x 60, a, prismatic lenses ; b, cuticle ; c, part of free cheek. E, lialmanUes 

 i-iili/n i-ix. Salt. Part of eye, x 30. F, Duliiuinites imbricatidits, Ang. Vertical 

 section of eye, with a part of the free cheek on the left, x 60. G, H, 7/ff ;/< 

 rii/utus, Burr. G, The two lenses of one eye, x 8 ; H, vertical section of the same, 



x60. 



continuous over the entire eye. Examples of this are seen in 

 /Inmteus and Spkaeropht/mf in //x. 



1 Liiulstrimi, "Visual Organs of Trilobites," Svensku- V<:t. Akad. Handl. xxxiv., 

 190-'l. Kxncr. rinjsinl. iJ . /<"<//. A iii/i'ii. r. A'ribfcti u. Iiixccten, 1891, p. 34, pi. ii. 

 is, 19. 



