BORRADAILE— ON THE PONTONIIN^ 327 



other features, M. SoUaud finds the following to indicate its nearness to the ancestral 

 form of the family : (1) the condition of the telson, (2) the retention of the larval 

 supraorbital spine, (3) the armature of the molar process*, which recalls that of the 

 primitive Acanthephhyra (Hoplophoridee), (4) the simple form of the epipodite of the 

 first maxilliped, which in most other Palsemonidse is bilobed, (5) the relation of 

 the propodite of the second maxilliped to the dactylopodite, which is here largely free, 

 instead of lying wholly alongside the propodite, (6) the armature of the fingers of the 

 chelae, which consists of fine spines arranged comb- wise, as in many Hoplophoridse and 

 Penseidse, and not of a cutting edge or coarse teeth, as in most Carides, (7) the gill-formula, 

 which comprises a pleurobranch for each leg and one for the third maxilliped, one 

 arthrobranch for the latter limb, and a podobranch on the second maxilliped. At the 

 same time, Desmocaris is not without features which constitute a departure from the 

 primitive state. As such may be cited (8) the loss of the mandibular palp, (9) the dis- 

 appearance of the cleft between the two divisions of the outer " lacinia " of the maxilla, 

 and (10) great reduction of the podobranch of the second njaxilla. 



The Palsemoninee are less primitive than Desmocaris in respect of the characters 

 numbered (l), (2), (3), (5), and (6) above, and most of them have a bilobed epipodite 

 on the first maxilliped, though in regard to (9), (10), and generally also to (8), they are 

 more primitive. The Typhlocaridinae are an aberrant branch of the False monine stock. 



On the other hand, the less specialized of the Pontoniinee are in many respects 

 near to the ancestral type. It is true that in the condition of the telson and of the 

 molar process t, and in the loss of the pleurobranch of the third maxilliped, all 

 Pontoniinse are unprimitive, but (a) many keep the supraorbital spine, (b) while nearly 

 all have lost the mandibular palp, Urocaridella and PalcemoneUa keep this structure, 

 though it is here of two joints, and not of three as in the Palsemoninse, (c) nearly 

 all have a double lacinia on the maxilla, (d) some have a simple epipodite to the first 

 maxilliped, and in many cases it is but slightly cleft, (e) some (belonging it is true 

 to the more modified genera Harpilius and Coralliocaris) have a free, or nearly free, 

 dactylopodite of the second maxilliped, (/) though the anterior pleurobranch is lost, 

 Urocaridella, and according to Nobili some Ancyclocaris, have a podobranch on the 

 second maxilliped, and {g) several species of Periclimenes have the comb arrangement 

 on the fingers of the first chela, and in at least one (P. denticidata) it is found also 

 on the second. Moreover [h) in the form of the outer flagellum of the antennule, 

 which is generally but slightly cleft, the Pontoniinee present a primitive feature not found 

 in either Desmocaris or the Palsemoninae. Since, however, this feature is in the present 

 subfamily found in the genera which are otherwise not primitive, it seems likely that 

 it is here not ancestral but a reversion. 



It would appear therefore that, though Desmocaris has departed least from the 

 structure of the ancestral palsemonid, the Pontoniinse left the main stem before the 

 evolution of the first representative of the Palsemoninse. 



* The molar surface is a plain, round area, about half of which is covered by toothed ridges. These 

 are probably an exceedingly primitive feature, for they are found in many Branchiopoda. 

 t But see below, p. 335. 



