WHITEAVES ] DKVONIAN FOSSILS OF MANITOBA, ETC. SflT) 



was collected by Mr. Tyrrell, in 1889, at South Manitou Island, Lake 

 Winiiipegosis, is very well preserved, although imperfect and somewhat 

 cruslied or distorted. It is nearly Hat but slightly convex abo\t', and 

 •shallowly concave below. As ^•iewed from a))ove, it consists of a central 

 tuberculatecl area, with a bix)ad and slightly bevelled outer margin devoid 

 of tubercles. The central tuberculated area, whose outei' limits are by 

 no means sharply defined, is longer- than l)road, .symmetrical, aud some- 

 what five sided, though the side which presumably represents the anterior 

 end of the plate and which therefore it will be convenient to call tlie 

 antero-median side, is shorter and narrower than any of the others, and 

 concavely and rather deeply emarginate, apparently to allow of the o\'er- 

 lap of the narrowly rounded posterior end of an antero-median ])late. 

 The two antero-lateral sides are at first nearly straight and parallel to the 

 hjngitudinal axis of the plate, but they are very slightly expanded about 

 the midlength and concavely contracted posteriorly. The two postero- 

 lateral sides are nearly straight and converge gradually and obliquely 

 until they meet at an acute angle in the centre posteriorly. The outer 

 and non-tuberculate margin is nearly two inches in breadth at its broadest 

 part. 



The surface markings (jf the central area consist of numerous small, 

 smooth and rounded tubercles, which are unequal in size and ii'regular in 

 their distribution, though the largest average two millijnetres in diameter 

 at the base, and from two to five millimetres in their distance apart at 

 the summits. The gi-eater part of the bevelled outer margin is smotitli 

 to the naked eye, but around its outer limits there are indications of shcart 

 and irregular radiating groo\-es and ridges. 



The actual length of the central tuberculated portion of the specimen, 

 as measured in the median line, is l(i7 millimetres: the approximate 

 V^readth of the .same, at the lateral angles, is about 11.'^ mm. The maxi- 

 mum thickness of the test is six mm. 



The genus Asjnilii-litliijs^ Newberry, was Ijased upon a single dors( i-median 

 plate, of gigantic dimensions, which is stated* to be "similar in form to 

 that of PtfiicJithi/K, h-at many times larger" and to be " co\ ered with 

 large hemispherical, sn)ooth, enamelled tubercles." " The most .stiiking 

 feature in this plate," I>r. Newberry says,t " is its external ornamentation. 

 This consists of knobs or bosses of smooth, shining enamel, of the size 

 and form of split peas. In its general aspect this tuberculation resembles 

 that of /'/I'l-ichflii/s or Oornoatcun, but ditfei-s strikingly in this, that the 

 tubercles are perfectly smooth and polished, and show nothing of the 



*Rep. Geol. Surv. Ohio, vol. T, pt. ■>, Palieont., (1873), p. .S22. 

 tibid., p. 32S. 



