278 Reviews — Revision of some Pliacopid Genera. 



(3) Polyamma burdekinensis, n.g. and n.sp., is compared with the 

 Canadian Silurian Helicotoma (?) spinosa, Salter, and with Triassic 

 and Silurian species referred to Ccelocentrus, Zittel, but as the single 

 specimen does not display the characters of the aperture and base its 

 systematic position is left undetermined. The figures are " a trifle 

 larger than natural size", but the exact dimensions of the specimen 

 are not given. 



(4) Yetofistula mirabiiis, n.g. and n.sp., from the Middle Devonian, 

 is compared with Phabdomeson, Young & Young, aud Chilatrypa, 

 Ulrich, and is provisionally referred to the family Rhabdomesontidae, 

 and still more hesitatingly to a sub-family for which the name 

 Yetofistuliporidge {sic) is proposed. 



Y. — Revision of some Phacopid Genera.. By F. H. McLearn. 

 Ottawa Naturalist, xxxii, pp. 31-6, 1918. 



SEVERAL genera of the Phacopid Trilobites are re-defined and 

 their phylogenetic relationships are discussed. Dalmanitina, 

 Reed, is extended to include a series of generalized forms extending 

 from the Ordovician through the Silurian. In the Devonian this 

 line gives rise to species forming the genus Phacopina, J. M. Clarke, 

 which, however, does not belong to the sub-family Phacopinae but 

 to the Dalmanitina?. The Phacopinae originated at the beginning of 

 the Silurian as an offshoot from the primitive line, and gave rise to 

 two stocks. One of these forms the genus Phacops, s.str., of wide 

 distribution in the Silurian and extending into the Devonian ; the 

 other, Phacopidella, Reed, is confined to the later Silurian of 

 Bohemia. 



YI. — The Phtlogeny of the Acorn Barnacles. By Rudolf 

 Ruedemann. Proc. ]S"at. Acad. Sci. Washington, iv, pp. 382-4, 

 1918. 



Possible Derivation of the Lepadid Barnacles from the 

 Phyllopods. By John M. Clarke. T.c, pp. 384-6. 



ONE of the most characteristic features of the Cirripedia is the 

 possession of an armature of shelly plates developed by the 

 calcification of separate areas in the "mantle", which represents 

 the shell-fold or carapace of other Crustacea. It is characteristic of, 

 but not peculiar to, the Phyllocarida that certain portions of the 

 carapace are separated by suture-lines — a movable rostrum in the 

 receDt forms and an additional dorsal plate in certain fossil genera. 

 YVith little more than these facts to go upon, Mr. Ruedemann 

 endeavours to show that the Cirripedia, and in particular the sessile 

 or operculate forms, have been derived from the Phyllocarida. 

 He mentions an undescribed genus, Eobalanus (no specific name is 

 given), from the Upper Ordovician, in which the form of the five 

 pairs of lateral compartments suggests a bivalved carapace, and he 

 ingeniously compares this with the carapace of certain Devonian 

 Phyllocarida. As in many fossil Cirripedia, the opercular valves, 

 scuta and terga, have been lost, and these valves, the most persistent 

 of all throughout the group, are neglected in Mr. Ruedemann's 



