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Vuiversitif of California Publications in Zoology [Vol.16 



Our attention has been called by Braus (1906) to an additional 

 rudimentary arch in the embryo of Ilcptanchus cinereus. Such an 

 arch is represented in text-figure B by the piece split off on the left 

 side from the ceratobranchial (c&*). But a more interesting condition 

 obtains on the right side. It will be observed that a slight asymmetry 

 is shown in text-figure B, which gives a somewhat greater develop- 

 ment in the mid-ventral region on the right than on the left side. 

 Through this asymmetry the rudimentary arch and adjoining area 

 on the right side are more highly developed than on the left. 



Upon examination of the ventral side of the rudimentary arch 

 of the right side I found certain rays (r., text-fig. C) arising from the 



Fig. C. Area of rudimentary arches, Eeptanclius maculatus. Camera lucida 

 outline, ventral view. 



a)»., evidence of a ninth arch; r., rudimentary rays; .r., part of eighth arch. 



seventh ceratobranchial practically at right angles to its long axis. 

 These extended posteriorly between the piece X and the median piece. 

 These are round and pointed and are of clear hyalin cartilage. I 

 am not certain whether they represent rudimentary branchial rays on 

 the seventh arch like those described by Gegenbaur (1872, pi. 12, 

 fig. 5) on the anterior margin of the fifth arch for ScylUum, or whether 

 they have to do with the rudimentary arch following. 



On the middle piece a similar arrangement is found. Here there 

 are three pieces which are successively longer toward the middle 

 line. They are e.s.sentially identical in appearance with those above 

 described on the seventh ceratobranchial segment, but they are attached 

 along their whole dorsal length as flattened lamellae. Terminally the 



