130 P. H. CAEPENTEE ON TWO NEW CEINOIDS EEOM 



to the Apiocrinidae is in the nature of the faces of the stem-joints, 

 which resemble those of Bourgueticrinus and Bhizocrinus. But 

 similar joints occur in the larval Antedon and in Platycrinus * ; so 

 that this resemblance does not go for much, especially when it is 

 remembered that d'Orbigny speaks of the articular faces of the 

 stem-joints in the Apiocrinidae as being most frequently marked 

 with radiating striae f. 



On the other hand, Mesocrinus differs from the Apiocrinidae as 

 defined by d'Orbigny and by Zittel t, in the presence of verticils of 

 cirrhi on the stem, and in the small size of its upper joints. 

 Further, the central funnel of the calyx (PI. YI. fig. 7 a) is small, 

 not wide and patent ; while the articular faces of the radials are 

 large, and not separated or barely in contact, but meet one another 

 along the whole length of their sides, and bear distinct fossae for 

 the attachment of muscles and ligaments. Ail these characters are 

 more or less distinctive of the type of the Pentacrinidae ; but Meso- 

 crinus cannot be referred to that family, as it lacks the petaloid 

 markings on the faces of the stem-joints. 



Mesoceintjs, n. g. 



Calyx more or less conical, composed of five basals forming a 

 complete ring, and five radials with high articular faces which bear 

 distinct muscular and ligament-fossae, and are in contact for the 

 whole length of their sides. Upper stem-joints the smallest. Lower 

 ones with elliptical faces, the long axes of which are occupied by 

 articular ridges. The planes of these ridges on the two faces of 

 each joint are more or less inclined to one another. The joints 

 may bear single cirrhi, or two may combine to form a node for a 

 verticil of two cirrhi. Eadicular cirrhi at the base of the stem. 



^Iesoceinus suedicus, n. sp. (Plate YI. fig. 7.) 



The lower part of the calyx is formed by five pentagonal basals, 

 which are in complete contact laterally, so as entirely to cut off the 

 radials from the top stem-joint. The lower surface of the basal 

 pentagon is very concave, with a large central perforation ; but it 

 is quite simple and devoid of any kind of ornamentation (PI. YI. 

 fig. 7b). The radials have very high outer surfaces (nearly twice as 

 high as the basals), which slope very slightly upwards and outwards. 

 Their articular faces are also rather high and trapezoidal, with large 

 muscle-plates standing up around the central funnel. The thickened 

 edges of the two muscle-plates on each radial are separated by a 

 slight intermuscular notch. The transverse ridge expands into a 

 large articular surface perforated by the opening of the central canal, 

 to which it forms a thick rim on all sides. Prom this surface short 

 ridges proceed upwards and outwards, separating the large muscle- 

 fossae from the small ligament-fossae. The dorsal fossa for the 

 elastic ligament is relatively small, being represented by little more 



* A Natural History of the Orinoidea (Bristol, 1821), pp. 34, 75* 

 t Op. cit. p. 1. 



% Handbuch der Palaontologie, Band i. p» 388* 



