372 



THE PLAGIOSTOMIA. 



Malacorhina. 



Malacorhina Garman, 1877, Proc. Bost. soc. nat. hist., 19, p. 203. 



Disk rhomboid, type with three rounded lobes. Pectorals extended in 

 front of the cranium, where they are narrowly separated by the snout, which is 

 slightly produced. No rostral cartilage in front of the skull. Mouth transverse, 

 waved; teeth small, numerous. Ventral fins deeply notched; claspers of males 

 tapering, pointed. Tail depressed, with lateral folds, two dorsals, and a rudi- 

 mentary caudal. Closely allied to Raia and Psammobatis. 



In the type movable cartilages above the proximal extremity of the hyo- 

 mandibular, Plate 69, fig. 1, x, with the spiracular, complete the foremost arch of 

 eight arches, and prove that at one time in the early history of the mouth the 

 upper jaws and the mentioned cartilages formed an arch with a suspensorium 

 distinct from that of the lower jaws, in other words, that the mouth was formed 

 of the anterior cleft of seven clefts five of which are now the gill openings. It 

 indicates also that the presence of six gill clefts in certain Platosomia, Pliotrema, 

 is, as in different sharks, Hexeptranchidae and Chlamydoselachidae, an ancestral 

 feature rather than an effect of specialization. 



Malacorhina mira. 

 Plate 27, fig. 3-5; Plate 69, fig. 1-2 (skeleton). 

 Raia (Malacorhina) mira Garman, 1877, Proc. Best. soc. nat. hist., 19, p. 207. 



Disk rhomboid, each anterior margin in two convex portions separated by a 

 decided notch; or the disk may be described as somewhat trilobed, with an 

 anterior and two lateral sections each broadly rounded. Snout produced, 

 unsupported by a rostral cartilage. Mouth transverse, undulated, width nearly 

 equal length of snout; teeth sharp in the median series, in || rows. Eyes mod- 

 erate, prominent, lids curved outward. Spiracles larger than the eyes. Anterior 

 portion of \entrals smaller, narrow; claspers strong in the base, tapering, pointed. 

 Disk with scattered small scales, larger opposite the eyes. Narrow, hooked 

 tubercles in an irregular vertebral series, behind the head and on the tail, inter- 

 rupted above the abdomen, smaller ones at each side of the median; tail rough. 

 Male with several elongate rows of erectile hooks near the outer edge of each 

 pectoral. Nostrils farther from one another than from the edges of the disk; 

 valves as in Raia. Dorsal fins near the end of the tail separated by a short 

 space. 



