426 CRUSTACEA ENTOMOSTRACA. 



coalesced with the carina and rostrum to form one unsymmetrical ring 

 of 4 plates, resembling the testa of other Operculata. The four species 

 of the genus Verruca which constitute the living representatives of this 

 family present a remarkable departure from the bilateral symmetry 

 characteristic of other Cirripedes. Superficially the shell appears to be 

 formed on the same plan as in other Operculata, but the operculum 

 which lies in the aperture of the shell is formed of the scutum and 

 tergum of one side only, those of the other side having taken their 

 places in the outer wall of the shell, which is completed by the carina 

 and rostrum. The prehensile antennae of the larva are situated at about 

 the middle of the (membranous) basis of the shell, but the body of the 

 animal, which is symmetrical about its own median plane, lies on its side, 

 with that plane parallel to the surface of attachment. The early larval 

 stages are symmetrical and the terga and scuta of opposite sides are alike 

 at their first formation. The lobes of the caudal fork are unusually long. 

 The shape, mode of growth and articulation of the tergum and scutum 

 show affinities with the Lepadidae. The shells are generally attached to 

 living bodies and are found down to a depth of 90 fathoms, from Iceland 

 to Cape Horn. V. stromia (O. Mull.) is British. A fossil species is 

 found in the Chalk. 



Sub-order 2. ACROTHORACICA. 



Minute Cirripedes of separate sexes. The females are enclosed in a 

 flask-shaped mantle beset with chitinous points and live in hollows which 

 they excavate in the shells of Molluscs. The thoracic appendages of the 

 first pair are palpiform or rudimentary, and two to four pairs of cirriform 

 feet are borne at the posterior end of the body. The intermediate appen- 

 dages are absent. Mouth parts and alimentary canal usually well 

 developed (the latter ends blindly in Alcippe). The males where known 

 are dwarfed, without alimentary canal, and spend their short existence 

 attached to the mantle of the female. 



The genus Cryfitophialus was placed in a distinct order of Cirripedes, 

 the Abdominalia, by Darwin on the indication afforded by the apparent 

 segmentation of the body. As seven segments appear to intervene be- 

 tween that bearing the maxillipeds (first thoracic) and the region from 

 which the three pairs of biramous appendages, at the posterior end of 

 the body, arise, it seemed evident that the latter could not be homologous 

 with the 4th, 5th and 6th thoracic appendages ofi other Cirripedes. 

 There are however reasons for not regarding the apparent segments as 

 indicative of the true segmentation. The disc by which the adult is at- 

 tached to its burrow must include, at its anterior end, the region from 

 which the first antennae of the pupa sprang (the 1st antennary segment) ; 

 yet the disc is borne on the apparent segment posterior to that bearing 

 the maxillipeds together with the other oral appendages. Hence, in the 

 anterior part, the apparent is no guide to the true segmentation.* The 

 close resemblance between Cryptophialus and Alcippe was fully recognized 

 by Darwin, and the subsequent discovery of Lithoglyptes and Kochlorine 



* The same argument applies to Proteolepas, the representative of the 

 following sub-order. In it the larval antennae persist throughout life, 

 and are borne behind the mouth on the second ring as indicated by the 

 superficial appearance of segmentation. 



