Notices of Memoirs — E. P. Quain — Mock- Sections Exhibited. 563 



the middle of the neck divides its superior aspect into two oblique 

 moderately convex surfaces. Other individuals show that this ridge 

 was prolonged down the back and tail, but less elevated. The body 

 is about as long as the neck. On the right side it has suffered some 

 abrasion and injury in cleaning, and is not quite symmetrical, being 

 a little larger on the left side. It is about 2*4 centim. wide, convex 

 from side to side, and less convex in length. The expansion from 

 the neck is rapid, and attenuation posteriorly is marked so that the 

 body has a long egg shape. The tail appears to be short and conical, 

 and curves rapidly downward in every sjjecimen. The height of the 

 body was not more than half its width. The limbs are imperfectly 

 preserved. Tlie distance between them on the left side is 2'4 centim. 

 The anterior limb appears to be the larger. The entire length of the 

 specimen is 12"5 centim. 



This individual lies over the neck of another specimen which was 

 larger, and appears to have measured 15 centim. without the head. 

 It shows the fore limbs to have been very wide relatively to their 

 length, and to have measured in the antero-posterior direction I'l 

 centim. at the junction with the shoulder on the right side; it is 

 flattened, extended horizontally, imperfect distally, and curved some- 

 what backward, but evidently short as compared with the adult. 

 The hind limbs of this specimen are not seen. 



Other individuals are smaller, and have the body only about half 

 as wide. They are very narrow in the anterior part of the body, 

 and there appears to be only a slight budding of the fore limbs. 



Hence, I regard this specimen as showing that the Plesiosaurus 

 was viviparous, and that in one species from the Lias many were 

 produced at one birth. The species was probably a long-necked one, 

 and may have been P. homalospondi/liis, since the head in young 

 animals is relatively large, and here it is ^ of the total length of the 

 animal. 



V. — Upon a Simple Method op Projecting upon the Screen 

 Microscopic Rock Sections both by Ordinary and by Polarized 

 Light. By E. P. Quain. ^ 



KNOWING the difficulty experienced in pointing out to students 

 any particular crystal in a rock-section when viewed with the 

 microscope direct, I attempted to project the images on the screen, 

 and by the aid of comparatively simple apparatus met with very 

 gratifying success, both with ordinary and with polarized light. 



The tube of the microscope was screwed out and replaced with 

 a cork, through which a hole had been cut to carry the ordinary 

 one-inch micro-objective and behind it the analyser of the micro- 

 scope. The polariscope and rock-section occupied their usual 

 position, as when used with the microscope in the ordinary way. 

 The microscope stand being inclined into the horizontal position was 

 placed in front of the object-lens of the lime-light lantern. The 

 object-lens of a lantern usually consists of a combination of two 

 lenses. If so, the back lens is taken out, and the front lens only 



1 Abstract of a paper read before the British Association, Manchester, Sept. 1887- 



