. The Canadian field-naturalist. Natural history. 1917 The Ottawa Naturalist. 77 WAS THE LOWER CAMBRL\X TRILOBITE SUPREME?* By Lancaster D. Burling. A new species of Lower Cambrian trilobite, Paedeumias robsonen- sis, has recently been described''" from a single specimen which is unique among the thousands of specimens of known trilobites in its imperfection. The reason for the extraordinary perfection of the tests of previoush" discovered trilobites has apparently escaped critical observation though the late development of the ability to roll up into a ball has been appealed to as i
. The Canadian field-naturalist. Natural history. 1917 The Ottawa Naturalist. 77 WAS THE LOWER CAMBRL\X TRILOBITE SUPREME?* By Lancaster D. Burling. A new species of Lower Cambrian trilobite, Paedeumias robsonen- sis, has recently been described''" from a single specimen which is unique among the thousands of specimens of known trilobites in its imperfection. The reason for the extraordinary perfection of the tests of previoush" discovered trilobites has apparently escaped critical observation though the late development of the ability to roll up into a ball has been appealed to as indicating that the trilobite was the supreme arbiter of the early Cambrian seas and needed no such pro- tection. He has recently been deposed from this position, however, at least for the ISIiddle Cambrian, and his title conferred upon Sidneyia inexpectans Walcottt, a Merostome-like crustacean which has been described as armed with a truly formidable set of chelate appendages or claws (see figure 2). In the Lower Cambrian, however, nothing has hitherto been discovered that would dispute the claim of the trilobite to be the largest inhabitant of the seas, and the specimen of Paedeumias above mentioned is as large or larger than any other fossil so far discovered in the lower Cambrian rocks of the North- western Cordillera. It is further noteworthy in having the greatest number of ribs (44) ever discovered in a trilobite. Fifteen of these are of large size and their long spines almost completely encircle the remaining 29 (or more, the end is broken off) which are smaller and nearly equal in Fig. 1—Paedeumias robsonensis Burling. Outline of right half of the first seven ribs, showing extent ot injury. As can be .seen by the photo- graph reproduced on plate I. Vol. XXX, opp. p. , the left half of these ribs is normal, with the exception that the fifth is slightly .shorter than the fourth and sixth. The enlargement of the third rib is characteristic of the family to whic
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