NO. 3 CASSIDULOID ECHINOIDS — KIER 79 



marginal periproct, and in having double-pored phyllodes and no 

 buccal pores. It differs mainly in shape, being almost square in 

 marginal outline, but this difference is not of sufficient importance to 

 justify generic distinction of this species. 



Genus PYGAULUS Agassiz 



Pygaulus L. Agassiz in L. Agassiz and Desor, 1847. Am. Sci. Nat., ser. 3, 

 vol. 7, p. 158. Type species by subsequent designation, Cotteau, 1869, Pal. 

 franc, Jur., p. 124, Pygaulus desmoulinsii Agassiz. 



GENERIC DESCRIPTION 



IMedium size, elongate, sides usually parallel, anterior and posterior 

 margins rounded, adapically highly inflated, cylinder shaped, apical 

 system anterior, tetrabasal ; petals broad, open or slightly closed, 

 petal III shorter than others, poriferous zones narrow, tapering 

 distally, pores conjugate, interporiferous zones very wide, all am- 

 bulacral plates double pored; periproct inframarginal, longitudinal; 

 peristome large, oval or oblique ; bourrelets slightly developed ; phyl- 

 lodes slightly widened or not widened, double pored, pores arranged 

 in two series in each half-ambulacrum; no buccal pores; tubercles 

 only slightly larger adorally. 



Comparison zvith other genera. — Pygaulus is very similar to Pygo- 

 rhynchus. Species of both genera have similar petals, an oblique 

 peristome, phyllodes with approximately the same number of pore 

 pairs in each series, and a longitudinal periproct. They are distin- 

 guished by the shape of the test and location of the periproct. In 

 Pygaulus, the test is generally high, with a smoothly rounded anterior 

 and posterior margin, parallel sides, and inframarginal periproct. In 

 Pygorhynchus, the test is generally lower, the anterior margin is 

 blunted, the posterior pointed, with the sides not parallel but expand- 

 ing posteriorly, resulting in the greatest width being posterior to the 

 center. The periproct is more marginal in position. These differences 

 are not very significant, and there is little doubt that these two genera 

 are closely related. 



Pygaulas is also very similar to Plagiochasma, having an almost 

 identical petal arrangement, peristome, and floscelle, but differing 

 in having an inframarginal instead of supramarginal periproct, and a 

 more cylindrical test. 



Remarks. — I have included (text fig. 63) a drawing of a phyllode 

 of Pygaulus morloti Desor. The specimen illustrated was figured by 

 De Loriol (1873, pi. 17, figs, i, 3) and is in his collection at the 



