252 



Fam. 2. Balanidæ. 



Gen. Balanns, Brug. 

 82. Balanus crenatus. Brug., varietas. 



(Pl. XX, Fig. 14, lo). 



Den her afbildede Balanus afviger i det ydre saa 

 paafaldende fra den for Balanerne sædvanlige pyramidale 

 riler patellalignende Form. at man mindst skulde tænke, 

 at den lod sig henføre til nogen af vore bekjendte Former. 

 Og dog har en nøiere Undersøgelse af Skallens Valvler 

 overbevist mig om, at den alene er at betragte som en 

 excessiv udviklet Varietet af den ved vore Kyster ikke ual- 

 mindeligt forekommende B. crenatus Brug. Som man vil 

 se, er det væsentlig den eiendommelige Udvikling af de 

 Kalkplader eller Valvler. der tilsammen danner Skallens 

 Væg iparietas), som udmærker denne Varietet og giver 

 Skallen et saa i høi Grad fremmed Udseende. Derimod 

 er de Valvler. der begrændser Aabningen (Tergalstykkerne 

 og Skjoldene) saavel i Form som Sculptur nøiagtigt af samme 

 Udseende som hos den sædvanlige Form af B. crenatus. 

 Skalvæggenes abnorme Udvikling hos den her omhandlede 

 Form tør maaske forklares derved, at Individerne fra først 

 af har været stærkt sammentrængte paa et forholdsvis lidet 

 Ruin og under sin paafølgende Væxt saaledes har været 

 nødt til at skyde i Veiret for at faa Ruin. I Darwins 

 Arbeide over Cirripederne er givet en Afbildning af en 

 Varietet af den her omhandlede Art, som tydeligt nærmer 

 sig til den her Fig. 15 afbildede Form, skjøndt paa langt 

 nær ikke visende en saadan excessiv Forlængelse af Skal- 

 væggen. Fig. 14 forestiller et af de mindre stærkt for- 

 længede Individer, der imidlertig endnu mærkeligt afviger 

 fra det typiske Udseende ved Skalvæggens cylindriske opad 

 noget ndvidede Form. 



Forekomst. Af nærværende eiendommelige Varietet 

 toges under Expeditionens sidste Togt nogle Exemplarer 

 ved Hjælp af Bundskraben paa Stat. 322, N af Beeren 

 Eiland, fra et Dyb af 21 Favne, haard Bund. 



Fam. 2. Balanidæ. 



Gen. Balanus, Brug. 

 82. Balanus crenatus, Brug., varietas. 



(Pl. XX, figs. 14. 15). 



The specimen of Balanus represented in the Plate, 

 exhibits so striking a deviation in its outer habitus from 

 the pyramidal or patelliform aspect usually distinguishing 

 the Balanidæ, that few would imagine it referable to any 

 one of the previously known forms. And vet a closer ex- 

 amination of the valves of the shell. has convinced me, 

 that the animal in question should be regarded as a mere 

 exceptionally developed variety of B. crenatus Brug., a spe- 

 des occurring not infrequently off the Norwegian coasts. 

 As will be seen, it is chiefly the peculiar development of 

 the calcareous plates, or valves, that together constitute the 

 wall of the shell (parietas), which distinguish this variety, 

 giving to the shell an aspect so characteristically alien. 

 On the other hand, the valves that define the opening 

 (the terga! segments and the shields) have alike in form and 

 in sculpture precisely the same appearance as those of the. 

 usual form B. crenatus. The abnormal development of 

 the wall of the shell in the form treated of here, will, 

 maybe, admit of explanation by assuming the individuals to 

 have been originally subjected to strong compression in a 

 relatively confined space, thus compelling theni. during the 

 progress of growth, to force an upward passage, for the 

 purpose of obtaining space. In Darwin 's work on the Cir- 

 ripedia. thereis a drawing of a variety of the species treated 

 of here, clearly approximating the form represented in fig. 

 15, though far from exhibiting so remarkable a prolonga- 

 tion of the wall of the shell. Fig. 14 gives one of the 

 less elongated individuals, which however still deviates 

 a good deal from the typical appearance, by reason of the 

 cylindric form — somewhat expanded, as it is. in an up- 

 ward direction — distinguishing the wall of the shell. 



Oceurrence. — Of the present peculiar variety, a 

 few specimens were brought up in the dredge. on the last 

 cruise of the Expedition, — at Station 322, north of 

 Beeren Eiland. from a depth of 21 fathoms: hard bottom. 



