1 98 Proceedin<fs of the Royal Irish Acadeni!/. 



length. The joiniiug iu- the upper bmuch or eudopodite (r^) was very 

 ditticult to trace iu places, so that it is possible that this l.aauch is couiposed 

 of uineteen segments, whereas the eighteen segments of tlie lower branch or 

 exopodite (rj> were beautiftiUy preserved and readily counted. 



Many of the joint.« bore long bristles or setae (s), and it is clearly 

 indicated that in life all the joints must have carried such setae, which were 

 doubtless ciliated, tlnis serving to help the animals in swimming and to waft 

 the plankton, on which these creatures feed, into their mouths. 



Antennae of other si>ecimens, as those figured on I'lateXXIV, fig. 2, and 

 te.xl-fig. 5a, show the presence of short stt.nt spines on the upper side of the 

 organ (Plate XX I Y. fig. 2a sp.). Thus not only in general appearance, but 

 also in details of structure, the antenna of Limuestheria is remarkably 

 similar to the antenna of the living Estheria. The beautiful state of 

 pi^servation of these delicate biramous oigans first attracted the attention 

 of one of the officers of the Geological Survey to this interesting appendage 

 material. 



MamUU'- (V\a.\.i: XXIV, fig. 1;. — In this specimen the mandibles were 

 not well preserved, but the impression of one (md.) showed distinctly near 

 the head region and nlxive the anlcnnae. The mandible is simple, oval 

 or sickle-shajied. and presumably strongly chilinised, without any evidence 

 of pjilps. It is articulat<Ml to the head by a triangular base. 



Mandibles were found iu at leasl five other si>ecimens, and are seen in 

 figure* 2b, .5a. Plate XXIV. tig. 1, and Plate XXV, figs. 1, 2 \ 4. 



The Trunk (Plate XXIV, fig. 1) —The segmentation of the body is not 

 well preserved, so that we cannot say of how many parts it is composed; 

 but in several specimens other than that taken as type the segmentation could 

 be made out, though poorly, as is indicated on Plate XXV, fig. 1. The dorsal 

 margin of each segment, at least in the posterior region, is produced into a 

 backwardly directe<l keel-shaped process, which probably carried spines 

 (Plato XXIV, fig. 1 ; Plate XXV, fig. 6). Similar keeled prolongations of 

 the segments are depicted by Packard in his engraN-ing of Estheria morsei 

 (Packard),' and they are also doubtless comi»ardble to the lamellar dorsal 

 ] = borne by the eight posterior segment* in Cyclestheria hislopi,- 



ihese latter, may aid in retaining the eggs within the shell (cf. also 

 text-figs. lA, 2a. Plate XXV, fig. 6). 



' A. S. I'vCK-iRii, Jr. k Monogrnph of the Phyllc.pod Crustacea of North America, 

 with remarks on the order Phylloc*ricU . U.S. Geol. Surv. Wy<,niiDg and Idaho, 1878. 

 Part I. 



= G. O. Sa»8: On Cydesthena hislopi (Baird), a new generic tyi>e of BivaWe 

 Phyllopoda. Forh. Vidcnakab-selsk. i. KrifltuaU, 1887. 



