and on Nehalia, and its Allies. 347 



in the diagnosis of a fossil, we have most readily and gladly corrected 

 such error when our attention has been drawn to it. 



(3.) In the third conclusion, "that even those forms which cannot 

 be referred to Aptychi of Cephalopods, are in no case the shields of 

 Phyllopods," Herr Dames is simply stating a matter of opinion ; for 

 of their exact nature and true zoological position Glaus himself (to 

 whom he seems to refer) is not at all positive, whilst Dames admits 

 that he has not examined the original specimens. 



As an illustration of unsupported dogmatic assertion, take the 

 following paragraph in reference to the body-rings of Discinocaris ; 

 " Even if the structures observed are really body-rings, no stronger 

 proof against their phyllopod nature could be brought forward ; for 

 the body-rings, as well as all the other parts, of the Phyllopod 

 (except the shell), are too tender and fragile to remain recognizable 

 in beds of such great age " ^ (Dames, op. cit.). 



In the presence of the long array of Insect-remains, of the most 

 delicate and fragile character, discovered in the Devonian and 

 Carboniferous formations, from North America, France, England, 

 Belgium, Bohemia, and elsewhere, this argument against the possi- 

 bility of delicate organisms being preserved falls to the ground ; 

 whilst the relative thickness and durability of the calcareous or 

 chitinous covering of the body-segments in these ancient Crustacea 

 afford no proof for or against their Phyllopod nature, any more 

 than does their relatively greater size when contrasted with existing 

 Entomostraca. Moreover, body-rings of Ceratiocaris are by no 

 means rare in some Silurian strata. 



I have long held the opinion that the expanded disc-like shields 

 such as Peltocaris, Discinocaris, AptycJiopsis, and some others, were 

 probably related ancestrally to the larval or adult forms of Phyllo- 

 pods like Apiis, Lepidurus, etc., whilst the relationship between the 

 living Nehalia and the numerous genera of Paleozoic pod-shrimps, 

 does not necessarily preclude us from considering these forms as 

 still belonging to the Entomostraca, although they may be placed 

 in Packard's order Phyllocarida (see infra). 



As to the question of ornamentation, upon which Herr Dames 

 insists so strongly, the concentric striae, marking lines of growth, 

 appear to me to correspond most closely in character and origin 

 with the similar decoration observable on the valves of Estheria, 

 Limnadia, etc., so that their absence upon the carapaces of Apus 

 and Nehalia does not necessarily prove that shields so ornamented 

 cannot be deemed to belong to Crustacea or even to the Phtllopoda ; 

 whilst many of the carapaces of the fossil genera, e.g. Dithjrocaris, 

 Ceratiocaris, etc., have either concentric or anastomosing stri» 



1 Prof. A. von Koenen, replying to Herr Dames, on behalf of Mr. J. M. Clarke, 

 very justly observes, " I cannot see that this at all meets the argument, since the 

 relative age of strata is of altogether little influence on the preservation of fossils ; 

 on the other hand, there are plenty of examples in which fossil animals have been 

 furnished with hard, horny and even calcareous parts which are wanting in their 

 nearest recent analogues. I will only recall here Aptychus and Anaplychus, von 

 Koenen." (N. Jahrbuch ii. Bd. i. Heft. 1884, p. 45.) ^ 



• The recent NauUhts has a fleshy hood ; the fossil Ammonite had usually a hard calcareous 

 operculum, but in some Liassic forms the operculum was horny. 



