PACKAUD] THE ORDER PHYLLOCARIDA. 445 



we have obtained more precise explanations as to the nature of their 

 limbs. 



"It is in the highest degree probable, however, that all these forms 

 are not true Phyllopods, but have belonged to a type of Crustacea, of 

 which now there are no living representatives, but which, taking their 

 origin from forms allied to the lower types of Eutomostraca, have pre- 

 pared the way for the Malacostracan type. Such a connecting link, which 

 has served to the present day, we evidently find in the genus Nebalia.'''' 



In 1879,^ without knowing the views of Clans, just quoted, we pub- 

 lished the following brief notice of the leading characteristics of the 

 groui), and proposed that the paleozoic fossil forrns, Ceratiocaris, etc., 

 be united with the ISTebaliaclse to form a separate order of Crustacea 

 under the name of Phyllocarida. 



"The Nehaliadw, represented by the existing genus Nehalia, have 

 generally been considered to form a family of Phyllopod Crustacea. 

 Metschnikoff, who studied the embryology of Nehalia, considered it to 

 be a 'Phyllopodiform Decapod.' Besides the resemblance to the Deca- 

 pods, there is also a combination of Copepod and Phyllopod character- 

 istics. The type is an instance of a generalized one, and is of high an- 

 tiquity, having been ushered in during the earliest Silurian Period, 

 when there were, when we regard the relative size of most Crustacea, 

 and especially of living Nehaliw, gigantic forms. Such was DitJiyro- 

 caris, which must have been over a foot long, the carapace being 7 inches 

 long. The modern Nehalia is small, about half an inch in length, with 

 the body compressed, the carapace bivalved as in Limnadia, one of the 

 genuine Phyllojjods. There is a large rostrum overhanging the head; 

 stalked eyes; and, besides two pairs of antennae and mouth parts, eight 

 pairs of leaf-like, short, respiratory feet, which are succeeded by swim- 

 ming feet. There is no metamorphosis, develoijment being direct. 



" Of the fossil forms, Rymenocaris was regarded by Salter as ' the more 

 generalized type.' The genera Feltocaris and Discinocaris characterize 

 the Lower Silurian Period, Geratiocaris the Upper, Dictyocaris the Up- 

 per Silurian and the lowest Devonian strata, Bithyrocaris and Argus the 

 Carboniferous Period. Our existing northeastern species is Nebalia 

 hipes (Fabricius), which occurs from Maine to Greenland. 



"The ISTebaliads were the forerunners of the Decapoda, and form, we 

 believe, the type of a distinct order of Crustacea, for which the name 

 Phyllocarida is proposed." 



A slightly fuller account of the order was also published in the 

 writer's Zoology,* and the order Phyllocarida was placed (pp. 325, 326) 

 below Tetradecapods and Decapods, the scheme then presented ibeing 

 on the following page : 



On examining the figures of Salter and of Barrande, for we have been 

 unable to study any of the fossils themselves owing to their extreme 

 rarity, the relationship to Nebalia is very marked, as seen in the form 

 of the carapace, the nearly free or detached rostrum, unless the separa-- 

 tion took place after the death of the animal, and also of the rather long, 

 slender abdomen. Upon examining the appendages at the end of the ab- 

 domen there is to bS seen an important distinction from Nebalia ; a long, 

 slender telson is usually present, with a single pair of large caudal sty- 

 lets, or cercopoda, in form like those of Nebalia. But in Hymenocaris 

 and Feltocaris the telson appears to be represented by a pair of small 



1 The Nebaliad Crustacea as types of a new order. By A. S. Packard, jr. American 

 Naturalist, February, 1879, vol. XIII, p. 128. . 



2 American Science Series. Zoology for High Schools and Colleges, 1st edition, 

 1879. 12°. H. Holt & Co., New York. 



