104 MEMOIR VI. 



Taking a general view of the existing Phyllopoda, they present us 

 with two distinct types, the one, Apus (PI. 6, f. 3), with the series of 

 members, numerous (upwards of 20) and close, the first pair consti- 

 tuting a trifid kind of rowers or feelers, the eleventh bearing on each 

 side a bivalve oviferous cell ; the body in this type is covered in great 

 part by a dorsal clypeus, attached only to the head, furnished with a 

 pair of approximate sessile eyes above, and with a pair of minute 

 antennae beneath ; to this type the Eyed Trilobites Calymena and 

 Asaphus most approximate, the principal difference being in the 

 comparatively short Clypeus, covering only the head and mouth, 

 and in the posterior part terminating with the last pair of members, 

 and not being produced into a tail ; as we know nothing of the 

 structure of the under side of these fossils, which is invariably en- 

 gaged in the rock upon which they repose, it remains undetermined 

 whether they were provided with rowers and antennae, it is certain, 

 however, that the Dudley Trilobite is sometimes accompanied by 

 subulate jointed bodies, which have been supposed the remains of 

 these members.* The other type, Artemis, (PI. 1), has eleven con- 

 cordant members, less closely set, a tail of eight joints, no clypeus 

 whatever, peduncled moveable eyes, conspicuous antennae, Bnd both 

 sexes with a pair of horns, or rather appendages, sometimes remark- 

 ably large in the male, smaller in the female, which has a single 

 oviferous sac attached beneath to near the root of the tail ; to this 

 type the existing Genera of Branchipus, Eulimena and Chieroceph- 

 alus belong, with an approximation in the fossil Genera of Buceph- 

 alithus (PL 5, f. 1, % 3), Ogygia (PI. 6, f. 1, 2), and Paradoxides, 

 (PI. 5, f. 4, 5, &c.) ; these differ, however, from the existing race 

 much in the same manner as the former type, in the want of a tail, 

 as well as in the members being much more numerous. Linnaeus 

 has given a figure of Bucephalithus Spinulosus with antennae, the 

 existence of which may be presumed, together with that of the pe- 

 dunculate eyes, which have not as yet however been noticed even 

 detached. 



What principally distinguishes this tribe of Crustacea, is the total 

 deprivation of proper feet, which are entirely converted into a kind 

 of leaf-like complicated fins, solely adapted to swimming, hence the 

 term Apus applied to one of the Genera. We shall be the less sur- 

 prized at this, when we recognize a similar conversion of feet into 

 fins even in some of the higher classes of animals, as, for example, 

 in the Trichecus of the Mammalia, the whole of the Cetacea, and in 

 the Mariiie Turtles. 



Of Artemis, or Brine Shrimp. 



The minute and rare animal which constitutes the type of this 

 (tcuus, being very imperfectly known, and consequently its place in 

 the class Crustacea indeterminable, induced me to procure some 

 from the Lymington Salt Pans, which was effected with considera- 

 ble difficulty, the fevv- that reached Cork being dead, and the Brine 



* It havino: been lately announeeil in several Journals, that an American Gentleman 

 had discovered and brought liome from the Falkland Islands, specimens of an animal 

 supposed to be the existing type of the Trilobites, I may just observe in the absence 

 of details, that the animals in question are most likely to be the Oniscus Paradoxus of 

 tlie Systema Naturie, " Antennis qiiaternis, searnentorum laterihiis falcalo spiitosis," 

 an inhabitant of the same seas near Terra del Fuego, juid long- ago pointed to, as pro- 

 bably related to the auiniul . in (piestion. 



