The hepato-pancreatic diverticula are directed posteriorly, and not anteriorly as in most Entomostraca, and the stomach is often furnished with chitinous teeth and ridges forming an elaborate gastric mill, especially in the larger Decapods. SERIES 1. LEPTOSTRACA. =Division. Phyllocarida.= [Illustration: FIG. 76.—_Nebalia geoffroyi_, ♀, × 20. _A.1_, _A.2_, 1st and 2nd antennae; _Ab.1_, _Ab.6_, 1st and 6th abdominal appendages; _A.G._ antennary gland; _C_, half of caudal fork; _E_, eye; _G_, ventral ganglionic chain; _H_, heart; _I_, intestine; _L_, upper liver-diverticulum; _M_, adductor muscle of halves of carapace; _MX_, palp of 1st maxilla; _O_, ovary; _R_, rostrum. (After Claus.) ] The small shrimp-like Crustacean _Nebalia_, which is found burrowing in the superficial layers of sand in the littoral and sometimes the deeper regions of most seas, has been regarded, ever since its anatomy was made out by Claus,[85] as a connecting link between Entomostraca and Malacostraca, and has been placed in a separate group Leptostraca. The segmentation of the body is Malacostracan, save that two extra segments are present in the abdomen, and the paired compound eyes are borne upon stalks. The eight thoracic limbs are all very similar; they are built on the typical biramous plan, and each carries a bract; they have been compared, owing to their flattened, expanded shape, to the foliaceous limbs of the Phyllopods. The abdominal appendages are also biramous. The heart is greatly elongated, stretching through thorax and abdomen; there are present both the antennary excretory glands characteristic of adult Malacostraca and the maxillary glands characteristic of adult Entomostraca, and both the posterior and anterior livers characteristic of the two Orders respectively are present. This combination of characters justifies the belief that _Nebalia_ represents a primitive form, standing to some extent in an intermediate position between Entomostraca and Malacostraca, but it may be doubted if the special relationship to the Phyllopoda, claimed on the strength of the foliaceous appearance of the thoracic limbs, can be legitimately pressed. _Nebalia_ shows the clearest signs of relationship to the other primitive Malacostraca, and especially to the Mysidae, which it resembles not only in general form and in the essentially biramous character of its appendages, but also in many embryological points and in the similarity in development of the brood-pouch.[86] A large number of very ancient palaeozoic fossils are known which are placed provisionally with _Nebalia_ in the Division Phyllocarida, and some of these are no doubt closely related to the existing isolated genus. _Hymenocaris_ from the Cambrian. SERIES 2. EUMALACOSTRACA.