2 AUKIV rÖR ZOOLOGI. BAND 3. NiO 11. 



highly arohed cheek, with a characteristic Limuloid outline 

 and curvature. Along the ventral börder is a continuous 

 flange which increases slightly in breadth anteriorly. Po- 

 steriorly this flange is 2,5 millimeters wide, and increases to 

 3,2 millimeters wide anteriorly. A similar marginal flange 

 is characteristic of all the species of Limulus. In Limulus 

 Walchi there is a second flange, wider than the outer, or 

 marginal flange. This broad inner flange increases in width 

 anteriorly and extends up on to the cephalothorax, so as to 

 include the median simple eyes. The absence of this second 

 inner flange is a striking distinction between Limulus Na- 

 thorsti and Limulus Walchi. 



The fragment of Limulus Nathorsti on the outer curve 

 measiires 205 millimeters, and at the broadest part measures 

 95 millimeters in width on the curve. The specimen does not 

 include the large compound eye or any of the trilobed feat- 

 ures of the dorsal side of the cephalothorax. A slight wrink- 

 ling of the surface is seen at one portion, similar to wrink- 

 ling that I have seen on a specimen of Limulus Walchi in 

 IVfunich. It may indicate that the shell was recently acquired 

 af ter moulting and therefore somewhat soft. 



Completing the outline of the cephalothorax in comparison 

 with complete specimens of Limulus, this specimen must 

 h^ve had a width across the cephalothorax, in a straight 

 line, of approximately 250 millimeters, or a width measured 

 on the curve of the test of about 342 millimeters. On the 

 basis of comparative measurements, made on other species, 

 the cephalothorax must have had a length of approximately 

 196 millimeters, measured on the median line, and the whole 

 animal a length of some 495 millimeters. This would make 

 it a very large species, closely approaching the size of the 

 very large Limulus polyphemus given in the following table. 

 In size it is considerably surpassed by the 1 argest indi vidu als 

 of the Tertiary Limulus Decheni. 



IJmulus Nathorsti differs from L. priscus in its vastly 

 greater size. It differs from L. Walchi in the absence of the 

 second marginal flange, in its indicated higher test and also 

 in its size. Limulus maximus of the upper Jurassic is too 

 little known to make any comparisons. It approaches near- 

 est to Limulus Decheni of the upper Tertiary. It differs from 

 this species in the indicated greater height of the cephalo- 



