.so Mr. T. II. Withers on 



ancestors of the Scalpellidoe. Stramentum, on the otlier 

 hiiiid, constitutes a highly specialized and aberrant form. 

 Instead of developing a definite peduncle, it specialized in 

 the disposition and arrangement of its plates to form a 

 completely armoured shell. AVhen attached to its object, 

 usually an ammonite, the cirri would not have nearly so 

 much sweep and freedom of movement as in a j)ednncu- 

 late form. The subsequent splitting of the carina, and the 

 non-intersection or overlap of the plates along the outer 

 margins of the shell, was no doubt evolved to obtain that 

 freedom of movement, and this specialization, while giving a 

 temporary advantage, probably led to its extinction under 

 changing conditions ; and the fact that the two sides of the 

 shell were so easily parted would render it especially vulner- 

 able to its enemies. 



I'rof. Gruvei (1905), who has been followed by later 

 authors, has a different conception of the phylogenetic 

 position o( Stramentum {=Loricuia). He considers that the 

 first remains of cirripedes are represented by the fossils 

 7urrilc/jas,li. Woodward, and Plu/nn!i/es, Hurrande, and that 

 those fossils constitute the complete imbricated covering of 

 a primitive cirripede. The animal may be said to have been 

 enclosed in a scaly cylinder, which afforded protection to 

 the appendages and soft parts. lie considered that later the 

 upper row of plates were more specially developed to form 

 the capitulum and that the remaining rows remained 

 undifferentiated and served to form the peduncle, Loricuhi 

 is supposed to represent this second stage, and Prof. Gruvei 

 has given some very convincing figures, which have been 

 reproduced in the text-books, as to the structural relation- 

 ship of tlujst' two forms. He docs not refer at all to Arc/iteo- 

 Icjjiis or any other Jurassic cirripede. 



Apart from the fact tliat Turrilcpas may not be a cirripede, 

 it is quite clear that Prof. Gruvei has misunderstood the 

 structure of the example of T. ivriyhtianus figured by 

 Dr. 11. Woodward, and on u hich he based his figure. Instead 

 oj' Turrilepas having a laterally flattened shell with five rows 

 of plates on either side as given in GruveFs figure (see 

 text-fig. 1 a, b), the shell is subtriangular in transverse 

 section (sec text-fig. 1 a') and there are four rows of plates 

 only. In fact, the real structure of tlie two forms is so 

 fundamentally diflerent that it is difficult to imagine that 

 there can be any relationship between them. 



AVhile it is difficult therefore to see how Turi'ilepas could 

 give rise to a form like Loricula (text-fig. 2), there is little 

 doubt that certain of the stalked cirripcdes were evolved 



