1558 THE VOYAGE OF H.M.S. CHALLENGER. 



diagnosis: "Dictyocha, e familia Bacillariorum. Lorica simplex univalvis silicea, laxe 

 reticulata aut stellulata" {he. cit.). In my Monograph (1862, p. 271), I placed it in the 

 class Eadiolaria, supposing that it might be a simple form of Acanthodesmida, having 

 found only isolated siliceous pieces. Afterwards (in 1879) Richard Hertwig observed the 

 entire living bodj^, and demonstrated that the hollow siliceous pieces are scattered in 

 great numbers around a tripylean central capsule, which exhibits all the essential characters 

 of PhvEODARIA (Organismus d. Radiol., 1879, p. 89). Hertwig describes the position of 

 the numerous siliceous pieces in the surface of the extracapsular jelly-sphere so densely 

 aggregated, that they touch one another and produce the appearance of a reticulated 

 sphere. In two specimens, which I observed living (PI. 101, fig. 10), and in numerous 

 complete specimens which I found in the collection of the Challenger, the number of the 

 siliceous pieces was much smaller, and they were scattered irregularly in the surface of the 

 alveolate jelly-sphere, being separated by wide and unequal intervals. The regular position 

 seems to be that the basal rings lie tangentially in the spherical surface of the calymma, 

 whilst the bars of the reticulum are directed outwards, and the apical spine radially in 

 centrifugal direction. Very often two pieces are united by their basal rings in such a 

 manner that they form a little sphei-oidal fenestrated body (as in Distephanus, Stohr ; 

 compare p. 1550). The characteristic reticular skeleton-pieces of Dictyocha must be 

 derived from Mesocena ; from its simple siliceous ring (on one side of its plane), arise 

 two, three, or four (rarely more) bars, which become united to a loose framework (with 

 two, three, or four meshes). When this network assumes the form of a truncated pyramid 

 (with a central mesh on the apex), Dictyocha passes over into Distephamis. From the 

 corners of the original basal ring several radial spines usually arise in a centrifugal direc- 

 tion, and on the sides of these sometimes small teeth or thorns also run in a centripetal 

 direction. The number of the meshes and the separating rods is usually four, more rarely 

 two or three. The hollow rods are very thin, either cyhndrical or prismatic. As the 

 ascending rods alternate regularly with the corner-spines of the basal ring, we may call the 

 latter perradial, the former interradial. Ehrenberg has distinguished in his genus 

 Dictyocha not less than fifty species, thirty-five living and twenty-five fossU (ten species 

 both living and fossil). The greater part of these cannot be retained, as they are only 

 slight varieties or abnormalities of single pieces of the skeleton, such as very frequently 

 occur associated with the common regular forms in one and the same individual. Such 

 abnormal species are, e.g., Dictyocha abnormis, Dictyocha hinoculus, Dictyocha hijxirtita, 

 Dictyocha haliomma, Dictyocha hexathyra, Dictyocha sej^tenaria, &c. One species (Dicty- 

 ocha splendens), is the fenestrated calcareous body of a Holothurian. Of some other species 

 Ehrenberg has only given the name, but neither a description nor a figure {e.g., Dictyocha 

 horealis, Dictyocha cenostephania, Dictyocha compos, Dictyocha coronata, Dictyocha 

 socialis, Dictyocha specillum). A number of other species must he placed in the genera 

 Distephamis and Cannopilus, so that only eight of his species of true Dictyocha remain. 



