200 COXTRIBUTIONS TO CANADIAN PALAEONTOLOGY. 



li>ose, but the other two were found m place, in a pale yellowi.sh-bi'own 

 coloured or nearly white dolomite of Devonian ag'e, associated witli Strinij- 

 oreiJiiihiK. 



In 18811, a large number of specimens of a S] ili rrro.ipov r/i < i., which, in 

 the writer's judgment, are undoubtedly identical witli iS. /i^xsi'/fii/a, were 

 collected by Messrs. Tyrrell and Dowling at se\'eral localities on the 

 shores and islands of Dawson Bay, especially on its south-eastern shore, 

 at a point four or hve miles north of the mouth of Hhoal River, called 

 Whiteaves Point on Mr. Tyrrell's map. These specimens, .some of which 

 are in unusually tine condition, were oljtained in place, from a partly 

 ci>mpact and partly vesicular dolomite, also holding ,':lfi-t>i//<ici'/jIiiiJus. 

 The originals of all the figures on plate xxxiii are from Dawson Bay. 



At this locality the specimens are more or less curved or twisteil, espe- 

 cially near the base, the most curveil specimen collected being that rei>re 

 sented by hg. 6. They vary considerably in shape, size and proportions, 

 but they all enclose a large central (■••u-ity. In some specimens the contour 

 is subpyriforra (tigs. 1, and 10) aird the height not much greater than the 

 maximum breadth. Others, again, are suljconical (fig. 9), arcuate and 

 clulj-shaped (lig. <j), oi' even almost cylindrical (tig. 4), and the lattei', of 

 c<jurse, are much higher than Ijrcjad. 



The details of theii- structure have been carefully studied by Mr. L. M. 

 Lambe. He finds " that, with the exception of a ba.sal circlet and :i \exy 

 small area at the summit, the whole of the outei- surface of the organism 

 consi.sts of close fitting hexagonal plates, which are slightly convex on 

 their outer surface, arranged in alternating M'rtical rows, and that each 

 plate has a small rounded elevation or tubercle in the centre, as described 

 and figured by Phillips, Hinde and others. In addition to the ccnti'al 

 elevation, each <.if the hexagonal plates in tlie Dawson Bay specimens is 

 marked by a few lines of growth pai-allel to the periphery, as shown in 



The base of the organism is entirely closed, pointed and composed of 

 four longitudinally elojigated, five-sided plates, as represented in figs. T) 

 and 5a. These basal plates ai-e marked with sculpture lines similar to 

 those of the hexagonal plates, but in each of the basals the central or 

 subcentral portion is (ievelope(l into a compai'atively large })rotuberance. 



The external characters of the summit are not yet .satisfactorily known, 

 but in the only specimen in which any portion of it is preser\eil (fig. 1) 

 the appearance is as there indicated, and there aic no indications that the 

 summit was covered by hexagonal plates. 



The interior of the ffjssil presents the appeai'ance of a nmnber of inter- 

 locking, hollow crucifoi'm 'spicules,' each of which has its central and vmdi- 

 vided jiortion anchylosed to the centre of the inner surface of one of the 

 hexagonal plates. The four rays rjf each ' spicule' lie iu a plane paiulhd 



