Dr. J. W. Gregory — The Age of the Morte Slates. 61 



new species agrees fairly closely with the Devonian species 

 Modiomorpha subalata (Conr.) ; and the probabilities seem to be 

 that if the dentition be ever determined, the fossil will be found to 

 belong to the Devonian genus Modiomorpha rather than to the 

 typicall}'^ Silui'ian genus Modiolopsis. 



Dr. Hicks lays most stress on the specimens determined as 

 Stricklandinia lirnta, Sow., of which he has figured four examples, 

 viz., fig. 3, p. 267 ; and pi. x, figs. 6, 7, and 8. Of the four speci- 

 mens, that shown on fig. 8 may be left out of account, as it is a 

 smaller and less satisfactory specimen of the form shown in fig. 6, 

 with which it fully agrees ; while that drawn on pi. x, fig. 7 has 

 lost the upper part of the shell, so that its family position is inde- 

 terminable ; the dotted line on the plate which suggests the position 

 of the hinge-line and beak is hypothetical. 



The two remaining specimens show three characters — 



1. The hinge-line is recognizable in the specimen shown in fig. 3, 

 although it is not seen in the figure ; the hinge-line is straighter 

 than in the genus StricJcIandinia, and agrees rather with Orthotetes. 



2. The muscular impressions. A pair of scars are shown on pi. x, 

 fig. 6, which Dr. Hicks identifies as muscular impressions. If this 

 be correct, it tells strongly against the fossil being a StricMnndinia, 

 for the muscular scars are far too large and wide; they agree with 

 those of Orthotetes, especially with those of the subgenus Hippariomjx. 



3. The shape of the shell. The specimen that offers the most 

 reliable evidence as to the shape of the shell is shown in pi. x, 

 fig. 6. The specimen is much higher than it is broad (ratio 18 : 11) ; 

 whereas in adult Stricldandiuia lirata, the ratio of height to breadth 

 varies from 18 : 22 to 18 : 26. The fact that the height of the Morte 

 Slate specimen is twice as great as in Stricklandinia lirata, may be 

 explained as due to crushing. But if the height of the shell has 

 been increased and its width decreased by deformation, then the 

 muscular scars also must have their breadth decreased by deformation. 

 They are, however, already far too wide for StricJcIandinia ; so to 

 include the Morte Slate fossil in that genus, we must assume that 

 the crushing of the specimen rolled out the shell in one direction 

 and the muscular impressions at right angles to that direction. 



The evidence of the two specimens (fig. 3, and pi. x, fig. 6), 

 therefore, appears to me conclusive that they do not belong to 

 Stricklandinia. To what genus, then, do they belong? There is 

 a striking resemblance in form and in the nature of the muscular 

 impressions, as well as a general agreement in size and hinge-line, 

 between these specimens and that figured by Davidson as Orthis 

 hipparionix in his " Devonian Brachiopoda," pi. xvii, fig. 8. The 

 specimen shown in that figure belongs to a species which is probably 

 allied to one previously figured by Davidson (loc. cit., pi. v, fig. 8) 

 as Spirifera disjuncta var. giganfea. Davidson so named that figui'e 

 from the belief that his specimen Avas identical with the form named 

 by Sowerby Spirifera gigantea. In this Davidson appears to me to 

 have been in error. Sowerby's specimen was a Spirifera, whereas 

 the specimen which Davidson confused with it is either an Orthotetes 



